Karl Jennings knew he was going to die. He had a matter of hours to live and much to do.

There was no reprieve from the death sentence, not hereon the Moon, not with no communications in operation.

Even on Earth there were a few fugitive patches where, without radio handy, a man might die without the hand of his fellow man to help him, without the heart of his fellow man to pity him, without even the eye of his fellow man to discover the corpse. Here on the Moon, there were few spots that were otherwise.

Earthmen knew he was on the Moon, of course. He had been part of a geological expedition-no, selenological expedition! Odd, how his Earth-centered mind insisted on the 'geo-.'

Wearily he drove himself to think, even as he worked. Dying though he was, he still felt that artificially imposed clarity of thought. Anxiously he looked about. There was nothing to see He was in the dark of the eternal shadow of the northern interior of the wall of the crater, a blackness relieved only by the intermittent blink of his flash. He kept that intermittent, partly because he dared not consume its power source before he was through and partly because he dared not take more than the minimum chance that it be seen.

On his left hand, toward the south along the nearby horizon of the Moon, was a crescent of bright white Sunlight. Beyond the horizon, and invisible, was the opposite lip of the crater. The Sun never peered high enough over the lip of his own edge of the crater to illuminate the floor immediately beneath his feet. He was safe from radiation- from that at least.

He dug carefully but clumsily, swathed as he was in his spacesuit. His side ached abominably.

The dust and broken rock did not take up the 'fairy castle' appearance characteristic of those portions of the Moon's surface exposed to the alternation of light and dark, heat and cold. Here, in eternal cold, the slow crumbling of the crater wall had simply piled fine rubble in a heterogeneous mass. It would not be easy to tell there had been digging going on.

He misjudged the unevenness of the dark surface for a moment and spilled a cupped handful of dusty fragments. The particles dropped with the slowness characteristic of the Moon and yet with the appearance of a blinding speed, for there was no air resistance to slow them further still and spread them out into a dusty haze.

Jennings' flash brightened for a moment, and he kicked a jagged rock out of the way. He hadn't much time. He dug deeper into the dust.

A little deeper and he could push the Device into the depression and begin covering it. Strauss must not find it.

Strauss!

The other member of the team. Half-share in the discovery. Half-share in the renown.

If it were merely the whole share of the credit that Strauss had wanted, Jennings might have allowed it. The discovery was more important than any individual credit that might go with it. But what Strauss wanted was something far more, something Jennings would fight to prevent.

One of the few things Jennings was willing to die to prevent. And he was dying.

They had found it together. Actually, Strauss had found the ship or, better, the remains of theship; or, better still, what just conceivably might havebeen the remains of something analogous to a ship.

'Metal,' said Strauss, as he picked up something ragged and nearly amorphous. His eyes and face could just barely be seen through the thick lead glass of the visor, but his rather harsh voice sounded clearly enough through the suit radio.

Jennings came drifting over from his own position half a mile away. He said, 'Odd! There is no free metal on the Moon.'

There shouldn't be. But you know well enough they haven't explored more than one per cent of the

Moon's surface. Who knows what can be found on it?'

Jennings grunted assent and reached out his gauntlet to take the object.

It was true enough that almost anything might be found on the Moon for all anyone really knew. Theirs was the first privately financed selenographic expedition ever to land on the Moon. 'I'll l then, there had been only government-conducted shotgun affairs, with half a dozen ends in view. It was a sign of the advancing space age that the Geological Society could afford to send two men to the Moon for selenological studies only.

Strauss said, 'It looks as though it once had a polished surface.'

'You're right,' said Jennings. 'Maybe there's more about.'

They found three more pieces, two of trifling size and one a jagged object that showed traces of a seam.

'Let's take them to the ship,' said Strauss.

They took the small skim boat back to the mother ship.

They shucked their suits once on board, something Jennings at least was always glad to do. He scratched vigorously at his ribs and rubbed his cheeks till his light skin reddened into welts.

Strauss eschewed such weakness and got to work. The laser beam pock-marked the metal and the vapor recorded itself on the spectrograph. Titanium-steel, essentially, with a hint of cobalt and molybdenum.

That's artificial, all right,' said Strauss. His broad-boned face was as dour and as hard as ever. He showed no elation, although Jennings could feel his own heart begin to race.

It may have been the excitement that trapped Jennings into beginning, 'This is a development against which we must steel ourselves-' with a faint stress on 'steel' to indicate the play on words.

Strauss, however, looked at Jennings with an icy distaste, and the attempted set of puns was choked off. Jennings sighed. He could never swing it, somehow. Never could! He remembered at the University-

Well, never mind. The discovery they had made was worth a far better-pun than any he could construct for all Strauss's calmness.

Jennings wondered if Strauss could possibly miss the significance.

He knew very little about Strauss, as a matter of fact, except by selenological reputation. That is, he had read Strauss's papers and he presumed Strauss had read his. Although their ships might well have passed by night in their University days, they had never happened to meet until after both had volunteered for this expedition and had been accepted.

In the week's voyage, Jennings had grown uncomfortably aware of the other's stocky figure, his sandy hair and china-blue eyes, and the way the muscles over his prominent jawbones worked when he ate. Jennings, himself, much slighter in build, also blue-eyed, but with darker hair, tended to withdraw automatically from the heavy exudation of the other's power and drive.

Jennings said, 'There's no record of any ship ever having landed on this part of the Moon. Certainly none has crashed.'

'If it were a part of a ship,' said Strauss, 'it should be smooth and polished. This is eroded and, without an atmosphere here, that means exposure to micrometeor bombardment over many years.'

Then he did see the significance. Jennings said, with an almost savage jubilation, 'It's a non-human artifact. Creatures not of Earth once visited the Moon. Who knows how long ago?'

'Who knows?' agreed Strauss dryly.

'In the report-'

'Wait,' said Strauss imperiously. Time enough to report when we have something to report. If it was a ship, there will be more to it than what we now have.'

But there was no point in looking further just then. They had been at it for hours, and the next meal and sleep were overdue. Better to tackle the whole job fresh and spend hours at it. They seemed to agree on that without speaking.

The Earth was low on the eastern horizon, almost full in phase, bright and blue-streaked. Jennings looked at it while they ate and experienced, as he always did, a sharp homesickness.

'It looks peaceful enough,' he said, 'but there are six billion people busy on it.'

Strauss looked up from some deep inner life of his own and said, 'Six billion people ruining it!' Jennings frowned. 'You're not an Ultra, are you?'

Strauss said, 'What the hell are you talking about?'

Jennings felt himself flush. A flush always showed against his fair skin, turning it pink at the slightest upset of the even tenor of his emotions. He found it intensely embarrassing. He turned back to his food, without saying anything.

For a whole generation now, the Earth's population had held steady. No further increase could be afforded. Everyone admitted that. There were those, in fact, who said that 'no higher' wasn't enough; the population had to drop. Jennings himself sympathized with that point of view. The globe of the Earth was being eaten alive by its heavy freight of humanity.

But how was the population to be made to drop? Randomly, by encouraging the people to lower the birth rate still further, as and how they wished? Lately there had been the slow rise of a distant rumble which wanted not only a population drop but a selected drop-the survival of the fittest, with the self-declared fit choosing the criteria of fitness.

Jennings thought: I've insulted him, I suppose.

Later, when he was almost asleep, it suddenly occurred to him that he knew virtually nothing of Strauss's character. What if it were his intention to go out now on a foraging expedition of his own so that he might getsole credit for-?

He raised himself on his elbow in alarm, but Strauss wasbreathing heavily, and even as Jennings listened, the breathing grew into the characteristic burr of a snore.

They spent the next three days in a single-minded search for additional pieces. They found some. They found more than that. They found an area glowing with the tiny phosphorescence of Lunar bacteria. Such bacteria were common enough, but nowhere previously had their occurrence been reported in concentration so great as to cause a visible glow.

Strauss said, 'An organic being, or his remains, may have been here once. He died, but the micro-organisms within him did not. In the end they consumed him.'

'And spread perhaps,' added Jennings. That may be the source of Lunar bacteria generally. They may not be native at all but may be the result of contamination instead-eons ago.'

'It works the other way, too,' said Strauss. 'Since the bacteria are completely different in very fundamental ways from any Earthly form of micro-organism, the creatures they parasitized-assuming this was their source-must have been fundamentally different too. Another indication of extraterrestrial origin.'

The trail ended in the wall of a small crater.

'It's a major digging job,' said Jennings, his heart sinking. 'We had better report this and get help.'

'No,' said Strauss somberly. There may be nothing to get help for. The crater might have formed a million years after the ship had crash-landed.'

'And vaporized most of it, you mean, and left only what we've found?' Strauss nodded.

Jennings said, 'Let's try anyway. We can dig a bit. If we draw a line through the finds we've made so far and just keep on...'

Strauss was reluctant and worked halfheartedly, so that it was Jennings who made the real find. Surely that counted! Even though Strauss had found the first piece of metal, Jennings had found the artifact itself.

It was an artifact-cradled three feet underground under the irregular shape of a boulder which had fallen in such a way that it left a hollow in its contact with the Moon's surface. In the hollow lay the artifact, protected from everything for a million years or more; protected from radiation, from micrometors, from temperature change, so that it remained fresh and new forever.

Jennings labeled it at once the Device. It looked not remotely similar to any instrument either had ever seen, but then, as Jennings said, why should it?

There are no rough edges that I can see,' he said. 'It may not be broken.' There may be missing parts, though.'

'Maybe,' said Jennings, 'but there seems to be nothing movable. It's all one piece and certainly oddly uneven.' He noted his own play on words, then went on with a not-altogether-successful attempt at self-control. This is what we need. A piece of worn metal or an area rich in bacteria is only material for deduction and dispute. But this is the real thing-a Device that is clearly of extraterrestrial manufacture.'

It was on the table between them now, and both regarded it gravely. Jennings said, 'Let's put through a preliminary report, now.'

'No!' said Strauss, in sharp and strenuous dissent. 'Hell, no!'

'Why not?'

'Because if we do, it becomes a Society project. They'll swarm all over it and we won't be as much as a footnote when all is done. No!' Strauss looked almost sly. 'Let's do all we can with it and get as much out of it as possible before the harpies descend.'

Jennings thought about it. He couldn't deny that he too wanted to make certain that no credit was lost. But still-- He said, 'I don't know that I like to take the chance, Strauss.' For the first time he had an impulse to use the man's first name, but fought it off. 'Look, Strauss.' he said, 'it's not right to wait. If this is of extraterrestrial origin, then it must be from some other planetary system. There isn't a place in the Solar System, outside the Earth, that can possibly support an advanced life form.'

'Not proven, really,' grunted Strauss, 'but what if you'reright?'

Then it would mean that the creatures of the ship had interstellar travel and therefore had to be far in advance, technologically, of ourselves. Who knows what the Device can tell us about their advanced technology. It might be the key to-who knows what. It might be the clue to an unimaginable scientific revolution.'

That's romantic nonsense. If this is the product of a technology far advanced over ours, we'll learn nothing from it. Bring Einstein back to life and show him a microprotowarp and what would he make of it?'

'We can't be certain that we won't learn.'

'So what, even so? What if there's a small delay? What if we assure credit for ourselves? What if we make sure that we ourselves go along with this, that we don't let go of it?'

'But Strauss'-Jennings felt himself moved almost to tears in his anxiety to get across his sense of the importance of the Device-'what if we crash with it? What if we don't make it back to Earth? We can't risk this thing.' He tapped it then, almost as though he were in love with it. 'We should report it now and have them send ships out here to get it. It's too precious to-'

At the peak of his emotional intensity, the Device seemed to grow warm under his hand. A portion of its surface, half-hidden under a flap of metal, glowed phosphorescently.

Jennings jerked his hand away in a spasmodic gesture and the Device darkened. But it was enough; the moment had been infinitely revealing.

He said, almost choking, 'It was like a window opening into your skull. I could see into your mind.'

'I read yours,' said Strauss, 'or experienced it, or entered into it, or whatever you choose.' He touched the Device in his cold, withdrawn way, but nothing happened.

'You're an Ultra,' said Jennings angrily. 'When I touched this'-And he did so. 'It's happening again. I see it. Are you a madman? Can you honestly believe it is humanly decent to condemn almost all the human race to extinction and destroy the versatility and variety of the species?'

His hand dropped away from the Device again, in repugnance at the glimpses revealed, and it grew dark again. Once more, Strauss touched it gingerly and again nothing happened. said, lets not start a discussion, for God's sake. This thing is an aid to communication-a telepathic amplifier. Why not? The brain cells have each their electric potentials. Thought can be viewed as a wavering electromagnetic field of microintensities-'

Jennings turned away. He didn't want to speak to Strauss. He said, 'We'll report it now. I don't give a damn about credit. Take it all. I just want it out of our hands.'

For a moment Strauss remained in a brown study. Then he said, 'It's more than a communicator. It responds to emotion and it amplifies emotion.'

'What are you talking about?'

Twice it started at your touch just now, although you'd been handling it all day with no effect. It still has no effect when I touch it.'

'Well?'

'It reacted to you when you were in a state of high emotional tension. That's the requirement for activation, I suppose. And when you raved about the Ultras while you were holding it just now, I felt as you did, for just a moment.'

'So you should.'

'But, listen to me. Are you sure you're so right. There isn't a thinking man on Earth that doesn't know the planet would be better off with a population of one billion rather than six billion. If we used automation to the full-as now the hordes won't allow us to do-we could probably have a completely efficient and viable Earth with a population of no more than, say, five million. Listen to me, Jennings.

Don't turn away, man.'

The harshness in Strauss's voice almost vanished in his effort to be reasonably winning. 'But we can't reduce the population democratically. You know that. It isn't the sex urge, because uterine inserts solved the birth control problem long ago; you know that. It's a matter of nationalism. Each ethnic group wants other groups to reduce themselves in population first, and I agree with them. I want my ethnic group, our ethnic group, to prevail. I want the Earth to be inherited by the elite, which means by men like ourselves. We're the true men, and the horde of half-apes who hold us down are destroying us all. They're doomed to death anyway; why not save ourselves?'

'No,' said Jennings strenuously. 'No one group has a monopoly on humanity. Your five million mirror-images, trapped in a humanity robbed of its variety and versatility, would die of boredom-and serve them right.'

'Emotional nonsense, Jennings. You don't believe that. You've just been trained to believe it by our damn-fool equalitarians. Look, this Device is just what we need. Even if we can't build any others or understand how this one works, this one Device might do. If we could control or influence the minds of key men, then little by little we can superimpose our views on the world. We already have an organization. You must know that if you've seen my mind. It's better motivated and better designed than any other organization on Earth. The brains of mankind flock to us daily. Why not you too? This instrument is a key, as you see, but not just a key to a bit more knowledge. It is a key to the final solution of men's problems. Join us! Join us!' He had reached an earnestness that Jennings had never heard in him.

Strauss's hand fell on the Device, which flickered a second or two and went out.

Jennings smiled humorlessly. He saw the significance of that. Strauss had been deliberately trying to work himself into an emotional state intense enough to activate the Device and had failed.

'You can't work it,' said Jennings. 'You're too darned super-mannishly self-controlled and can't break down, can you?' He took up the Device with hands that were trembling, and it phosphoresced at once.

'Then you work it. Get the credit for saving humanity.'

'Not in a hundred million years,' said Jennings, gasping and barely able to breathe in the intensity of his emotion. 'I'm going to report this now.'

'No,' said Strauss. He picked up one of the table knives. 'It's pointed enough, sharp enough.'

'You needn't work so hard to make your point,' said Jennings, even under the stress of the moment conscious of the pun. 'I can see your plans. With the Device you can convince anyone that I neverexisted. You can bring about an Ultra victory.

Strauss nodded. 'You read my mind perfectly.'

'But you won't,' gasped Jennings. 'Not while I hold this.' He was willing Strauss into immobility.

Strauss moved raggedly and subsided. He held the knife out stiffly and his arm trembled, but he did not advance.

Both were perspiring freely.

Strauss said between clenched teeth, 'You can't keep it-up all-day.'

The sensation was clear, but Jennings wasn't sure he had the words to describe it. It was, in physical terms, like holding a slippery animal of vast strength, one that wriggled incessantly. Jennings had to concentrate on the feeling of immobility.

He wasn't familiar with the Device. He didn't know how to use it skillfully. One might as well expect someone who had never seen a sword to pick one up and wield it with the grace of a musketeer.

'Exactly,' said Strauss, following Jennings' train of thought. He took a fumbling step forward.

Jennings knew himself to be no match for Strauss's mad determination. They both knew that. But there was the skim boat. Jennings had to get away. With the Device.

But Jennings had no secrets. Strauss saw his thought and tried to step between the other and the skim boat.

Jennings redoubled his efforts. Not immobility, but unconsciousness. Sleep, Strauss, he thought desperately. Sleep! Strauss slipped to his knees, heavy-lidded eyes closing.

Heart pounding, Jennings rushed forward. If he could strike him with something, snatch the knife...

But his thoughts had deviated from their all-important concentration on sleep, so that Strauss's hand was on his ankle, pulling downward with raw strength.

Strauss did not hesitate. As Jennings tumbled, the hand that held the knife rose and fell. Jennings felt the sharp pain and his mind reddened with fear and despair.

It was the very access of emotion that raised the flicker of the Device to a blaze. Strauss's hold relaxed as Jennings silently and incoherently screamed fear and rage from his own mind to the other. Strauss rolled over, face distorted.

Jennings rose unsteadily to his feet and backed away. He dared do nothing but concentrate on keeping the other unconscious. Any attempt at violent action would block out too much of his own mind force, whatever it was; too much of his unskilled bumbling mind force that could not lend itself to really effective use.

He backed toward the skim boat. There would be a suit on board-bandages- The skim boat was not really meant for long-distance runs. Nor was Jennings, any longer. His right side was slick with blood despite the bandages. The interior of his suit was caked with it.

There was no sign of the ship itself on his tail, but surely it would come sooner or later. Its power was many times his own; it had detectors that would pick up the cloud of charge concentration left behind by his ion-drive reactors.

Desperately Jennings had tried to reach Luna Station on his radio, but there was still no answer, and he stopped in despair. His signals would merely aid Strauss in pursuit.

He might reach Luna Station bodily, but he did not think he could make it. He would be picked off first.

He would die and crash first. He wouldn't make it. He would have to hide the Device, put it away in a safe place, then make for Luna Station.

The Device...

He was not sure he was right. It might ruin the human race, but it was infinitely valuable. Should he destroy it altogether? It was the only remnant of non-human intelligent life. It held the secrets of an advanced technology; it was an instrument of an advanced science of the mind. Whatever the danger, consider the value-the potential value- No, he must hide it so that it could be found again-but only by the enlightened Moderates of the government. Never by the Ultras...

The skim boat flickered down along the northern inner rim of the crater. He knew which one it was, and the Device could be buried here. If he could not reach Luna Station thereafter, either in person or by radio, he would have to at least get away from the hiding spot: well away, so that his own person would not give it away. And he would have to leave some key to it's location.

He was thinking with an unearthly clarity, it seemed to him. Was it the influence of the Device he was holding? Did it stimulate his thinking and guide him to the perfect message? Or was it the hallucination of the dying, and would none of it make any sense to anyone? He didn't know, but he had no choice. He had to try.

For Karl Jennings knew he was going to die. He had a matter of hours to live and much to do.

* * *

H. Seton Davenport of the American Division of the Terrestrial Bureau of Investigation rubbed the star-shaped scar on his left cheek absently. 'I'm aware, sir, that the Ultras are dangerous.'

The Division Head, M. T. Ashley, looked at Davenport narrowly. His gaunt cheeks were set in disapproving lines. Since he had sworn off smoking once again, he forced his groping fingers to close upon a stick of chewing gum, which he shelled, crumpled, and shoved into his mouth morosely. He was getting old, and bitter, too, and his short iron-gray mustache rasped when he rubbed his knuckles against it.

He said, 'You don't know how dangerous. I wonder if anyone does. They are small in numbers, but strong among the powerful who, after all, are perfectly ready to consider themselves the elite. No one knows for certain who they are or how many.'

'Not even the Bureau?'

'The Bureau is held back. We ourselves aren't free of the taint, for that matter. Are you?' Davenport frowned. 'I'm not an Ultra.'

'I didn't say you were,' said Ashley. 'I asked if you were free of the taint. Have you considered what's been happening to the Earth in the last two centuries? Has it never occurred to you that a moderate decline in population would be a good thing? Have you never felt that it would be wonderful to get rid of the unintelligent, the incapable, the insensitive, and leave the rest. I have, damn it.'

'I'm guilty of thinking that sometimes, yes. But considering something as a wish-fulfillment idea is one thing, but planning it as a practical scheme of action to be Hitlerized through is something else.'

'The distance from wish to action isn't as great as you think. Convince yourself that the end is important enough, that the danger is great enough, and the means will grow increasingly less objectionable.

Anyway, now that the Istanbul matter is taken care of, let me bring you up to date on this matter. Istanbul was of no importance in comparison. Do you know Agent Ferrant?'

The one who's disappeared? Not personally.'

'Well, two months ago, a stranded ship was located on the Moon's surface. It had been conducting a privately financed selenographic survey. The Russo-America Geological Society, which had sponsored the flight, reported the ship's failure to report. A routine search located it without much trouble within a reasonable distance of the site from which it had made its last report.

'The ship was not damaged but its skim boat was gone and with it one member of the crew. Name-Karl Jennings. The other man, James Strauss, was alive but in delirium. There was no sign of physical damage to Strauss, but he was quite insane. He still is, and that's important.'

'Why?' put in Davenport.

'Because the medical team that investigated him reported neurochemical and neuroelectrical abnormalities of unprecedented nature. They'd never seen a case like it. Nothing human could have brought it about.'

A flicker of a smile crossed Davenport's solemn face. 'You suspect extraterrestrial invaders?'

'Maybe,' said the other, with no smile at all. 'But let me continue. A routine search in the neighborhood of the stranded ship revealed no signs of the skim boat. Then Luna Station reported receipt of weak signals of uncertain origin. They had been tabbed as coming from the western rim of Mare Imbrium, but it was uncertain whether they were of human origin or not, and no vessel was believed to be in the vicinity. The signals had been ignored. With the skim boat in mind, however, the search party headed out for Imbrium and located it. Jennings was aboard, dead. Knife wound in one side. It's rather surprising he hadlived as long as he did.

'Meanwhile the medico's were becoming increasingly dis turbed at the nature of Strauss's babbling. They contacted the Bureau and our two men on the Moon-one of them happened to be Ferrant-arrived at the ship.

'Ferrant studied the tape recordings of the babblings. There was no point in asking questions, for there was, and is, no way of reaching Strauss. There is a high wall between the universe and himself-probably a permanent one. However, the talk in delirium, although heavily repetitious and disjointed, can be made to make sense. Ferrant put it together like a jigsaw puzzle.

'Apparently Strauss and Jennings had come across an object of some sort which they took to be of ancient and non-human manufacture, an artifact of some ship wrecked eons ago. Apparently it could somehow be made to twist the human mind.'

Davenport interrupted. 'And it twisted Strauss's mind? Is that it?'

That's exactly it. Strauss was an Ultra-we can say "was" for he's only technically alive-and Jennings did not wish to surrender the object. Quite right, too. Strauss babbled of using it to bring about the self-liquidation, as he called it, of the undesirable. He wanted a final, ideal population of five million.

There was a fight in which only Jennings, apparently, could handle the mind-thing, but in which Strauss had a knife. When Jennings left, he was knifed, but Strauss's mind had been destroyed.'

'And where was the mind-thing?'

'Agent Ferrant acted decisively. He searched the ship and the surroundings again. There was no sign of anything that was neither a natural Lunar formation nor an obvious product of human technology. There was nothing that could be the mind-thing. He then searched the skim boat and its surroundings. Again nothing.'

'Could the first search team, the ones who suspected nothing-could they have carried something off?' They swore they did not, and there is no reason to suspect them of lying. Then Ferrant's partner--'

'Who was he?'

'Gorbansky,' said the District Head.

'I know him. We've worked together.'

'I know you have. What do you think of him?'

'Capable and honest.'

'All right. Gorbansky found something. Not an alien artifact. Rather, something most routinely human indeed. It was an ordinary white three-by-five card with writing on it, spindled, and in the middle finger of the right gauntlet. Presumably Jennings had written it before his death and, also presumably, it represented the key to where he had hidden the object.'

'What reason is there to think he had hidden it?'

'I said we had found it nowhere.'

'I mean, what if he had destroyed it, as something too dangerous to leave intact?'

That's highly doubtful. If we accept the conversation as reconstructed from Strauss's ravings-and

Ferrant built up what seems a tight word-for-word record of it-Jennings thought the mind-thing to be of key importance to humanity. He called it "the clue to an umimaginable scientific revolution." He wouldn't destroy something like that. He would merely hide it from the Ultras and try to report its whereabouts to the government. Else why leave a clue to its whereabouts?'

Davenport shook his head, 'You're arguing in a circle, chief. You say he left a clue because you think there is a hidden object, and you think there is a hidden object because he left a clue.'

'I admit that. Everything is dubious. Is Strauss's delirium meaningful? Is Ferrant's reconstruction valid? Is

Jennings' due really a clue? Is there a mind-thing, or a Device, as Jennings called it, or isn't there? There's no use asking such questions. Right now, we must act on the assumption that there is such a Device and that it must be found.'

'Because Ferrant disappeared?'

'Exactly.'

'Kidnapped by the Ultras?'

'Not at all. The card disappeared with him.'

'Oh-I see.'

'Ferrant has been under suspicion for a long time as a secret Ultra. He's not the only one in the Bureau under suspicion either. The evidence didn't warrant open action; we can't simply lay about on pure suspicion, you know, or we'll gut the Bureau from top to bottom. He was under surveillance.'

'By whom?'

'By Gorbansky, of course. Fortunately Gorbansky had filmed the card and sent the reproduction to the headquarters on Earth, but he admits he considered it as nothing more than a puzzling object and included it in the information sent to Earth only out of a desire to be routinely complete. Ferrant-the better mind of the two, I suppose-did see the significance and took action. He did so at great cost, for he has given himself away and has destroyed his future usefulness to the Ultras, but there is a chance that there will be no need for future usefulness. If the Ultras control the Device--'

'Perhaps Ferrant has the Device already.'

'He was under surveillance, remember. Gorbansky swears the Device did not turn up anywhere.'

'Gorbansky did not manage to stop Ferrant from leaving with the card. Perhaps he did not manage to stop him from obtaining the Device unnoticed, either.'

Ashley tapped his fingers on the desk between them in an uneasy and uneven rhythm. He said at last, 'I don't want to think that. If we find Ferrant, we may find out how much damage he's done. 'I'll l then, we must search for the Device. If Jennings hid it, he must have tried to get away from the hiding place. Else why leave a clue? It wouldn't be found in the vicinity.'

'He might not have lived long enough to get away.'

Again Ashley tapped, 'The skim boat showed signs of having engaged in a long, speedy flight and had all but crashed at the end. That is consistent with the view that Jennings was trying to place as much space as possible between himself and some hiding place.'

'Can you tell from what direction he came?'

'Yes, but that's not likely to help. From the condition of the side vents, he had been deliberately tacking and veering.'

Davenport sighed. 'I suppose you have a copy of the card with you.'

'I do. Here it is.' He flipped a three-by-five replica toward Davenport. Davenport studied it for a few moments. It looked like this:

Davenport said, 'I don't see any significance here.'

'Neither did I, at first, nor did those I first consulted. But consider. Jennings must have thought that Strauss was in pursuit; he might not have known that Strauss had been put out of action, at least, not permanently. He was deadly afraid, then, that an Ultra would find him before a Moderate would. He dared not leave a clue to open. This'-and the Division Head tapped the reproduction-'must represent a clue that is opaque on the surface but clear enough to anyone sufficiently ingenious.'

'Can we rely on that?' asked Davenport doubtfully. 'After all, he was a dying, frightened man, who might have been subjected to this mind-altering object himself. He need not have been thinking clearly, or even humanly. For instance, why didn't he make an effort to reach Lunar Station? He ended half a circumference away almost. Was he too twisted to think clearly? Too paranoid to trust even the Station? Yet he must have tried to reach them at first since they picked up signals. What I'm saying is that this card, which looks as though it is covered with gibberish, is covered with gibberish.'

Ashley shook his head solemnly from side to side, like a tolling bell. 'He was in panic, yes. And I suppose he lacked the presence of mind to try to reach Lunar Station. Only the need to run and escape possessed him. Even so this can't be gibberish. It hangs together too well. Every notation on the card can be made to make sense, and the whole can be made to hang together.'

'Where's the sense, then?' asked Davenport.

'You'll notice that there are seven items on the left side and two on the right. Consider the left-hand side first. The third one down looks like an equals sign. Does an equals sign mean anything to you, anything in particular?'

'An algebraic equation.'

That's general. Anything particular?'

'No.'

'Suppose you consider it as a pair of parallel lines?'

'Euclid's fifth postulate?' suggested Davenport, groping.

'Good! There is a crater called Euclides on the Moon-the Greek name of the mathematician we call Euclid.'

Davenport nodded. 'I see your drift. As for F/A, that's force divided by acceleration, the definition of mass by Newton's second law of motion--'

'Yes, and there is a crater called Newton on the Moon also.'

'Yes, but wait awhile, the lowermost item is the astronomic symbol for the planet Uranus, and there is certainly no crater-or any other lunar object, so far as I know-that is named Uranus.'

'You're right there. But Uranus was discovered by William Herschel, and the H that makes up part of the astronomic symbol is the initial of his name. As it happens, there is a crater named Herschel on the Moon-three of them, in fact, since one is named for Caroline Herschel, his sister, and another for John Herschel, his son.'

'Davenport thought awhile, then said, 'PC/2-Pressure times half the speed of light. I'm not familiar with that equation.'

'Try craters. Try P for Ptolemaeus and C for Copernicus.'

'And strike an average? Would that signifiy a spot exactly between Ptolemaeus and Copernicus?'

'I'm disappointed, Davenport,' said Ashley sardonically. 'I thought you knew your history of astronomy better than that. Ptolemy, or Ptolemaeus in Latin, presented a geocentric picture of the Solar System with the Earth at the center, while Copernicus presented a heliocentric one with the Sun at the center. One astronomer attempted a compromise, a picture halfway between that of Ptolemy and Copernicus--'

Tycho Brahe!' said Davenport.

'Right. And the crater Tycho is the most conspicuous feature on the Moon's surface.'

'AH right. Let's take the rest. The C-C is a common way of writing a common type of chemical bond, and I think there is a crater named Bond.'

'Yes, named for an American astronomer, W. C. Bond.'

The item on top, XY2. Hmm. XYY. An X and two Y's. Wait! Alfonso X. He was the royal astronomer in medieval Spain who was called Alfonso the Wise. X the Wise. XYY. The crater Alphonsus.'

'Very good. What's SU?' That stumps me, chief.'

'I'll tell you one theory. It stands for Soviet Union, the old name for the Russian Region. It was the Soviet Union that first mapped the other side of the Moon, and maybe it's a crater there. Tsiolkovsky, for instance. You see, then, the symbols on the left can each be interpreted as standing for a crater: Alphonsus, Tycho, Euclides, Newton, Tsiolkovsky, Bond, Herschel.'

What about the symbols on the right-hand side?'

That's perfectly transparent. The quartered circle is the astronomic symbol for the Earth. An arrow pointing to it indicates that Earth must be directly overhead.'

'Ah,' said Davenport, 'the Sinus Medii-the Middle Bay- over which the Earth is perpetuity at zenith. That's not a crater, so it's on the right-hand side, away from the other symbols.'

'All right,' said Ashley. Thenotations all make sense, or they can be made to make sense,so there's at least a good chance that this isn't gibberish and that it is trying to tell us something. But what?So far we'vegot seven craters and a non-crater mentioned, and what doesthat mean? Presum ably, the Device can only be in one place.'

'Well,' said Davenport heavily, 'a crater can be a huge place to search. Even if we assume he hugged the shadow to avoid Solar radiation, there can be dozens of miles to examine in each case. Suppose the arrow pointing to the symbol for the Earth defines the crater where he hid the Device, the place from which the Earth can be seen nearest the zenith.'

That's been thought of, old man. It cuts out one place and leaves us with seven pinpointed craters, the southernmost extremity of those north of the Lunar equator and the northernmost extremity of those south. But which of the seven?'

Davenport was frowning. So far, he hadn't thought of anything that hadn't already been thought of.

'Search them all,' he said brusquely.

Ashley crackled into brief laughter. 'In the weeks since this has all come up, we've done exactly that.'

'And what have you found?'

'Nothing. We haven't found a thing. We're still looking, though.'

'Obviously one of the symbols isn't interpreted correctly.'

'Obviously!'

'You said yourself there were three craters named Herschel. The symbol SU, if it means the Soviet Union and therefore the other side of the Moon, can stand for any crater on the other side: Lomonosov, Jules Verne, Joliot-Curie, any of them. For that matter, the symbol of the Earth might stand for the crater Atlas, since he is pictured as supporting the Earth in some versions of the myth. The arrow might stand for the Straight Wall.'

There's no argument there, Davenport. But even if we get the right interpretation for the right symbol, how do we recognize it from among all the wrong interpretations, or from among the right interpretations of the wrong symbols? Somehow there's got to be something that leaps up at us from this card and gives us so clear a piece of information that we can tell it at once as the real thing from among all the red herrings. We've all failed and we need a fresh mind, Davenport. What do you see here?'

'I'll tell you one thing we could do,' said Davenport reluctantly. 'We can consult someone I--Oh, my God!' He half-rose.

Ashley was all controlled excitement at once. 'What do you see?'

Davenport could feel his hand trembling. He hoped his lips weren't. He said. Tell me, have you checked on Jennings' past life?'

'Of course.'

'Where did he go to college?'

'Eastern University.'

A pang of joy shot through Davenport, but he held on. That was not enough. 'Did he take a course in extraterro-logy?'

'Of course, he did. That's routine for a geology major.'

'All right, then, don't you know who teaches extraterrology at Eastern University?' Ashley snapped his fingers. 'That oddball. What's-his-name -Wendell Urth.'

'Exactly, an oddball who is a brilliant man in his way. An oddball who's acted as a consultant for the

Bureau on several occasions and given perfect satisfaction every time. An oddball I was going to suggest we consult this time and then noticed that this card was telling us to do so. An arrow pointing to the symbol for the Earth. A rebus that couldn't mean more clearly "Go to Urth," written by a man who was once a student of Urth and would know him.'

Ashley stared at the card, 'By God, it's possible. But what could Urth tell us about the card that we can't see for ourselves?'

Davenport said, with polite patience, 'I suggest we ask him, sir.'

* * *

Ashley looked about curiously, half-wincing as he turned from one direction to another. He felt as though he had found himself in some arcane curiosity shop, darkened and dangerous, from which at any moment some demon might hurtle forth squealing.

The lighting was poor and the shadows many. The walls seemed distant, and dismally alive with book-films from floor to ceiling. There was a Galactic Lens in soft three-dimentionality in one corner andbehind it were star charts that could be made out A map of the Moon in another corner might, however, possibly be a map of Mars.

Only the desk in the center of the room was brilliantly lit by a tight-beamed lamp. It was littered with papers and opened printed books. A small viewer was threaded with film, and a clock with an old-fashioned round-faced dial hummed with subdued merriment.

Ashley found himself unable to recall that it was late afternoon outside and that the sun was quite definitely in the sky. Here, within, was a place of eternal night. There was no sign of any window, and the clear presence of circulating air did not spare him a claustrophobic sensation.

He found himself moving closer to Davenport, who seemed insensible to the unpleasantness of the situation.

Davenport said in a low voice, 'He'll be here in a moment, sir.'

'Is it always like this?' asked Ashley.

'Always. He never leaves this place, as far as I know, except to trot across the campus and attend his classes.'

'Gentlemen! Gentlemen!' came a reedy, tenor voice. 'I am so glad to see you. It is good of you to come.'

A round figure of a man bustled in from another room, shedding shadow and emerging into the light.

He beamed at them, adjusting round, thick-lensed glasses upward so that he might look through them. As his fingers moved away, the glasses slipped downward at once to a precarious perch upon the round nubbin of his snub nose. 'I am Wendell Urth,' he said.

The scraggly gray Van Dyke on his pudgy, round chin did not in the least add to the dignity which the smiling face and the stubby ellipsoidal torso so noticeably lacked.

'Gentlemen! It is good of you to come,' Urth repeated, as he jerked himself backward into a chair from which his legs dangled with the toes of his shoes a full inch above the floor. 'Mr. Davenport remembers, perhaps, that it is a matter of-uh-some importance to me to remain here. I do not like to travel, except to walk, of course, and a walk across the campus is quite enough for me.'

Ashley looked baffled as he remained standing, and Urth stared at him with a growing bafflement of his own. He pulled a handkerchief out and wiped his glasses, then replaced them, and said, 'Oh, I see the difficulty. You want chairs. Yes. Well, just take some. If there are things on them, just push them off.

Push them off. Sit down, please.'

Davenport removed the books from one chair and placed them carefully on the floor. He pushed the chair toward Ashley. Then he took a human skull off a second chair and placed the skull even more carefully on Urth's desk. Its mandible, insecurely wired, unhinged as he transferred it, and it sat there with jaw askew.

'Never mind,' said Urth, affably, 'it will not hurt. Now tell me what is on your mind, gentlemen?' Davenport waited a moment for Ashley to speak, then, rather gladly, took over. 'Dr. Urth, do you remember a student of yours named Jennings? Karl Jennings?'

Urth's smile vanished momentarily with the effort of recall. His somewhat protuberant eyes blinked. 'No,' he said at last. 'Not at the moment.'

'A geology major. He took your extraterrology course some years ago. I have his photograph here, if that will help.'

Urth studied the photograph handed him with nearsighted concentration, but still looked doubtful. Davenport drove on. 'He left a cryptic message which is the key to a matter of great importance. We have so far failed to interpret it satisfactorily, but this much we see-it indicates we are to come to you.'

'Indeed? How interesting! For what purpose are you to come to me?'

'Presumably for your advice on interpreting the message.'

'May I see it?'

Silently Ashely passed the slip of paper to Wendell Urth. The extraterrologist looked at it casually, turned it over, and stared for a moment at the blank back. He said, 'Where does it say to ask me?'

Ashley looked startled, but Davenport forestalled him by saying, The arrow pointing to the symbol of the Earth. It seems clear.'

'It is clearly an arrow pointing to the symbol for the planet Earth. I suppose it might literally mean "go to the Earth" if this were found on some other world.'

'It was found on the Moon, Dr. Urth, and it could, I sup pose mean that. However, the reference to you seemed clear once we realized that Jennings had been a student of yours.'

'He took a course in extraterrology here at the University?' That's right.'

'In what year, Mr. Davenport?'

'In '18.'

'Ah. The puzzle is solved.'

'You mean the significance of the message?' said Davenport.

'No, no. The message has no meaning to me. I mean the puzzle of why it is that I did not remember him, for I remember him now. He was a very quiet fellow, anxious, shy, self-effacing-not at all the sort of person anyone would remember. Without this'-and he tapped the message-'I might never have remembered him.'

'Why does the card change things?' asked Davenport.

The reference to me is a play on words. Earth-Urth. Not very subtle, of course, but that is Jennings. His unattainable delight was the pun. My only clear memory of him is his occasional attempts to perpetrate puns. I enjoy puns, I adore puns, but Jennings-yes, I remember him well now-was atrocious at it.

Either that, or distressingly obvious at it, as in this case. He lacked all talent for puns, yet craved them so much--'

Ashley suddenly broke in. This message consists entirely of a kind of wordplay, Dr. Urth. At least, we believe so, and that fits in with what you say.'

'Ah!' Urth adjusted his glasses and peered through them once more at the card and the symbols it carried. He pursed his plump lips, then said cheerfully, 'I make nothing of it.'

'In that case--' began Ashley, his hands balling into fists.

'But if you tell me what it's all about,' Urth went on, 'then perhaps it might mean something.'

Davenport said quickly, 'May I, sir? I am confident that this man can be relied on-and it may help.'

'Go ahead,' muttered Ashley. 'At this point, what can it hurt?'

Davenport condensed the tale, giving it in crisp, telegraphic sentences, while Urth listened carefully, moving his stubby fingers over the shining milk-white desktop as though he were sweeping up invisible cigar ashes. Toward the end of the recital, he hitched up his legs and sat with them crossed like an amiable Buddha.

When Davenport was done, Urth thought a moment, then said, 'Do you happen to have a transcript of the conversation reconstructed by Ferrant?'

'We do,' said Davenport. 'Would you like to see it?'

'Please.'

Urth placed the strip of microfilm in a scanner and worked his way rapidly through it, his lips moving unintelligibly at some points. Then he tapped the reproduction of the cryptic message. 'And this, you say, is the key to the entire matter? The crucial clue?'

'We think it is, Dr. Urth.'

'But it is not the original. It is a reproduction.'

'That is correct.'

The original has gone with this man, Ferrant, and you believe it to be in the hands of the Ultras.'

'Quite possibly.'

Urth shook his head and looked troubled. 'Everyone knows my sympathies are not with the Ultras. I would fight them by all means, so I don't want to seem to be hanging back, but-what is there to say that this mind-affecting object exists at all? You have only the ravings of a psychotic and your dubious deductions from the reproduction of a mysterious set of marks that may mean nothing at all.'

'Yes, Dr. Urth, but we can't take chances.'

'How certain are you that this copy is accurate? What if the original has something on it that this lacks, something that makes the message quite clear, something without which the message must remain impenetrable?'

'We are certain the copy is accurate.'

'What about the reverse side? There is nothing on the back of this reproduction. What about the reverse of the original?'

'The agent who made the reproduction tells us that the back of the original was blank.'

'Men can make mistakes.'

'We have no reason to think he did, and we must work on At least until such time as the original is regained.'

'Then you assure me,' said Urth, 'that any interpretation to be made of this message must be made on the basis of exactly what one sees here.'

'We think so. We are virtually certain,' said Davenport with a sense of ebbing confidence.

Urth continued to look troubled. He said, 'Why not leave the instrument where it is? If neither group finds it, so much the better. I disapprove of any tampering with minds and would not contribute to making it possible.'

Davenport placed a restraining hand on Ashley's arm sensing the other was about to speak. Davenport said, 'Let me put it to you. Dr. Urth, that the mind-tampering aspect is not the whole of the Device.

Suppose an Earth expedition to a distant primitive planet had dropped an old-fashioned radio there, and suppose the native population had discovered electric current had been not yet developed the vacuum tube.

The population might discover that if the radio was hooked up to a current, certain glass objects within it would grow warm and would glow, but of course they would receive no intelligible sound, merely, at best, some buzzes and crackles. However, if they dropped the radio into a bathtub while it was plugged in, a person in that tub might be electrocuted. Should the people of this hypothetical planet therefore conclude that the device they were studying was designed solely for the purpose of tilling people?'

'I see your analogy.' said Urth. 'You think that the mind tampering property is merely an incidental function of the Device?'

'I'm sure of it,' said Davenport earnestly. 'If we can puzzle out its real purpose, earthly technology may leap ahead centuries.'

Then you agree with Jennings when he said'-here Urth consulted the microfilm-' "It might be the key to-who knows what? It might be the clue to an unimaginable scientific revolution."'

'Exactly!'

'And yet the mind-tampering aspect is there and is infinitely dangerous. Whatever the radio's purpose, it does electrocute.'

'Which is why we can't let the Ultras get it.'

'Or the government either, perhaps?'

'But I must point out that there is a reasonable limit to caution. Consider that men have always held danger in their hands. The first flint knife in the old Stone Age; the first wooden club before that could kill. They could be used to bend weaker men to the will of stronger ones under threat of force and that, too, is a form of mind-tampering. What counts, Dr. Urth, is not the Device itself, however dangerous it may be in the abstract, but the intentions of the men who make use of the Device. The Ultras have the declared intention of killing off more than 99-9 per cent of humanity. The government, whatever the faults of the men composing it, would have no such intention.'

'What would the government intend?'

'A scientific study of the Device. Even the mind-tampering aspect itself could yield infinite good. Put to enlightened use, it could educate us concerning the physical basis of mental function. We might learn to correct mental disorders or cure the Ultras. Mankind might learn to develop greater intelligence generally.'

'How can I believe that such idealism will be put into practice?'

'I believe so. Consider that you face a possible turn to evil by the government if you help us, but you risk the certain and declared evil purpose of the Ultras if you don't.'

Urth nodded thoughtfully. 'Perhaps you're right. And yet I have a favor to ask of you. I have a niece who is, I believe quite fond of me. She is constantly upset over the fact that I steadfastly refuse to indulge in the lunacy of travel. She states that she will not rest content until someday I accompany her to Europe or North Carolina- or some other outlandish place--'

Ashley leaned forward earnestly, brushing Davenport's restraining gesture to one side. 'Dr. Urth, if you help us find the Device and if it can be made to work, then I assure you that we will be glad to help you free yourself of your phobia against travel and make it possible for you to go with your niece anywhere you wish.'

Urth's bulging eyes widened and he seemed to shrink within himself. For a moment he looked wildly about as though he were already trapped. 'No.'' he gasped. 'Not at all! Never!'

His voice dropped to an earnest, hoarse whisper. 'Let me plain the nature of my fee. If I help you, if you retrieve the Device and learn its use, if the fact of my help becomes public, then my niece will be on the government like a fury. She is a terribly headstrong and shrill-voiced woman who will raise public subscriptions and organize demonstrations. She will stop at nothing. And yet you must not give in to her. You must not! You must resist all pressures. I wish to be left alone exactly as I am now. That is my absolute and minimum fee.'

Ashley flushed. 'Yes, of course, since that is your wish.'

'I have your word?'

'You have my word.'

'Please remember. I rely on you too, Mr. Davenport.'

'It will be as you wish,' soothed Davenport. 'And now, I presume, you can interpret the items?'

The items?' asked Urth, seeming to focus his attention with difficulty on the card. 'You mean these markings, XY2 and so on?'

'Yes. What do they mean?'

'I don't know. Your interpretations are as good as any, I suppose.'

Ashley exploded. 'Do you mean that all this talk about helping us is nonsense? What was this maundering about a fee, then?'

Wendell Urth looked confused and taken aback. 'I would like to help you.'

'But you don't know what these items mean.'

'I-I don't. But I know what this message means.'

'You do?' cried Davenport.

'Of course. It's meaning is transparent. I suspected it halfway through your story. And I was sure of it once I read the reconstruction of the conversations between Strauss and Jennings. You would understand it yourself, gentlemen, if you would only stop to think.'

'See here,' said Ashley in exasperation, 'you said you don't know what the items mean.'

'I don't. I said I know what the message means.'

'What is the message if it is not the items? Is it the paper, for Heaven's sake?'

'Yes, in a way.'

'You mean invisible ink or something like that?'

'No! Why is it so hard for you to understand, when you yourself stand on the brink?'

Davenport leaned toward Ashley and said in a low voice, 'Sir, will you let me handle it, please?'

Ashley snorted, then said in a stifled manner, 'Go ahead.'

'Dr. Urth,' said Davenport, 'will you give us your analysis?'

'Ah! Well, all right.' The little extraterrologist settled back in his chair and mopped his damp forehead on his sleeve. 'Let's consider the message. If you accept the quartered circle and the arrow as directing you to me, that leaves seven items. If these indeed refer to seven craters, six of them, at least, must be designed merely to distract, since the Device surely cannot be in more than one place. It contained no movable or detachable parts-it was all one piece.

'Then, too, none of the items are straightforward. SU might, by your interpretation, mean any place on the other side of the Moon, which is an area the size of South America. Again PC/2 can mean "Tycho," as Mr. Ashley says, or it can mean "halfway between Ptolemaeus and Copernicus," as Mr. Davenport thought, or for that matter "halfway between Plato and Cassini." To be sure, XY2 could mean "Alfonsus"-very ingenious interpretation, that-but it could refer to some coordinate system in which the

Y coordinate was the square of the X coordinate. Similarly C-C would mean "Bond" or it could mean "halfway between Cassini and Copernicus." F/A could mean "Newton" or it could mean "between Fabricius and Archimedes."

'In short, the items have so many meanings that they are meaningless. Even if one of them had meaning, it could not be selected from among the others, so that it is only sensible to suppose that all the items are merely red herrings.

'It is necessary, then, to determine what about the message is completely unambiguous, what is perfectly clear. The answer to that can only be that it is a message, that it is a clue to a hiding place. That is the one thing we are certain about isn't it?'

Davenport nodded, then said cautiously, 'At least, we think we are certain of it.'

'Well, you have referred to this message as the key to the whole matter. You have acted as though it were the crucial clue. Jennings himself referred to the Device as a key or a clue. If we combine this serious view of the matter with Jennings' penchant for puns, a penchant which may have been heightened by the mind-tampering Device he was carrying--So let me tell you a story.

'In the last half of the sixteenth century, there lived a German Jesuit in Rome. He was a mathematician and astronomer of note and helped Pope Gregory XIII reform the calendar in 1582, performing all the enormous calculations required. This astronomer admired Copernicus but he did not accept the heliocentric view of the Solar System. He clung to the older belief that the Earth was the center of the Universe.

'In 1650, nearly forty years after the death of this mathematician, the Moon was mapped by another Jesuit, the Italian astronomer, Giovanni Battista Riccioli. He named the craters after astronomers of the past and since he too rejected Copernicus, he selected the largest and most spectacular craters for those who placed the Earth at the center of the Universe-for Ptolemy, Hipparchus, Alfonso X, Tycho Brahe.

The biggest crater Riccioli could find he reserved for his German Jesuit predecessor.

This crater is actually only the second largest of the craters visible from Earth. The only larger crater is Bailly, which is right on the Moon's limb and is therefore very difficult to see from the Earth. Riccioli ignored it, and it was named for an astronomer who lived a century after his time and who was guillotined during the French Revolution.'

Ashley was listening to all this restlessly. 'But what has this to do with the message?'

'Why, everything,' said Urth, with some surprise. 'Did you not call this message the key to the whole business? Isn't it the crucial clue?'

'Yes, of course.'

'Is there any doubt that we are dealing with something that is a clue or key to something else?'

'No, there isn't,' said Ashley.

'Well, then--The name of the German Jesuit I have been speaking of is Christoph Klau-pronounced "klow." Don't you see the pun? Klau-clue?'

Ashley's entire body seemed to grow flabby with disappointment. 'Farfetched,' he muttered.

Davenport said anxiously, 'Dr. Urth, there is no feature on the Moon named Klau as far as I know.'

'Of course not,' said Urth excitedly. That is the whole point. At this period of history, the last half of the sixteenth century, European scholars were Latinizing their names. Klau did so. In place of the German "u", he made use of the equivalent letter, the Latin "v". He then added an "ius" ending typical of Latin names and Christoph Klau became Christopher Clavius, and I suppose you are all aware of the giant crater we call Clavius.'

'But-' began Davenport.

'Don't "but" me,' said Urth. 'Just let me point out that the Latin word "clavis" means "key." Now do you see the double and bilingual pun? Klau-clue, Clavius-clavis- key. In his whole life, Jennings could never have made a double, bilingual pun, without the Device. Now he could, and I wonder if death might not have been almost triumphant under the circumstances. And he directed you to me because he knew I would remember his penchant for puns and because he knew I loved them too.' The two men of the Bureau were looking at him wide-eyed.

Urth said solemnly, 'I would suggest you search the shaded rim of Clavius, at that point where the Earth is nearest the zenith.'

Ashley rose. 'Where is your videophone?'

'In the next room."

Ashley dashed. Davenport lingered behind. 'Are you sure. Dr. Urth?'

'Quite sure. But even if I am wrong, I suspect it doesn't matter.'

'What doesn't matter?'

'Whether you find it or not. For if the Ultras find the Device, they will probably be unable to use it.'

'Why do you say that?'

"You asked me if Jennings had ever been a student of mine, but you never asked me about Strauss, who was also a geologist. He was a student of mine a year or so after Jennings. I remember him well.'

'Oh?'

'An unpleasant man. Very cold. It is the hallmark of the Ultras, I think. They are all very cold, very rigid, very sure of themselves. They can't empathize, or they wouldn't speak of killing off billions of human beings. What emotions they possess are icy ones, self-absorbed ones, feelings incapable of spanning the distance between two human beings.'

'I think I see.'

'I'm sure you do. The conversation reconstructed from Strauss's ravings showed us he could not manipulate the Device. He lacked the emotional intensity, or the type of necessary emotion. I imagine all Ultras would. Jennings, who was not an Ultra, could manipulate it. Anyone who could use the Device would, I suspect, be incapable of deliberate cold-blooded cruelty. He might strike out of panic fear as Jennings struck at Strauss, but never out of calculation, as Strauss tried to strike at Jennings. In short, to put it tritely, I think the Device can be actuated by love, but never by hate, and the Ultras are nothing if not haters.'

Davenport nodded. 'I hope you're right. But then-why were you so suspicious of the government's motives if you felt the wrong men could not manipulate the Device?'

Urth shrugged. 'I wanted to make sure you could bluff and rationalize on your feet and make yourself convincingly persuasive at a moment's notice. After all, you may have to face my niece.'

***

This story has even pleasanter memories for me than the one before. At the Twenty-fourth World Science Fiction Convention, held in Cleveland over the Labor Day weekend in 1966, I was one of those who received a Hugo (the 'Oscar' of science fiction fandom), under conditions of great satisfaction to myself, and with my wife and children in the audience to see. (I am grinning foolishly for sheer joy of recall as I type this.) The science fiction magazine IF also won a Hugo and its editor set about collecting promises from other Hugo winners to write stories for a special Hugo issue. I would have had to have a heart of obsidian not to promise-so I did. This is the result. It is the only story I know of to combine the mystery form with Einstein's General Theory of Relativity.