Lucky raised his eyebrows. "How did you find that out, Bigman?"

"I'm not so dumb, Lucky." The little Martian was grave and deadly serious. "Do you remember when we were heading down toward the south pole of Saturn and you got out of the ship? It was just before the Sirians spotted us and we had to hot-jet it for Cassini's division."

"Yes."

"You had a reason for doing that. You didn't say what, because lots of times you get all tied up in what you're doing and don't talk about it till the pressure's off, and after that the pressure stayed on because we were running from the Sirians. So when we were building the quarters for Wess on Mimas, I just looked over the outside of The Shooting Starr, and it became quite clear you'd been working on the Agrav unit. You've got it fixed so that you could blow the whole thing by touching the all-shift contact on the control panel."

Lucky said gently, "The Agrav unit is the one thing about the Shooter that's completely top-secret."

"I know. I figured if you'd counted on fighting you'd have known The Shooting Starr wouldn't quit till it and we were blasted out of space. Agrav unit and all. If you were fixing to blow up just the Agrav and leave the rest of the ship intact, it was because you weren't counting on fighting. You were going to surrender."

"And is this why you've been brooding since we landed on Mimas?"

"Well, I'm with you whatever you do, Lucky, but" -Bigman sighed and looked away-"surrendering is no fun."

"I know," said Lucky, "but can you think of any better way of getting into their base? Our business, Bigman, isn't always fun." And Lucky touched the all-shift contact on the control panel. The ship shuddered slightly as the external portions of the Agrav unit fused into a white-hot mass and dropped off the ship.

"You mean you're going to bore from within? Is that the reason for the surrender?" "Part of it."

"Suppose they blast us down as soon as they get us?"

"I don't think they will. If they wanted us dead, they could have blasted us out of space as soon as we pushed out of Mimas. I have a notion they can use us alive... And if we're kept alive, we now have Wess on Mimas as a kind of backstop. I had to wait until we had arranged that before I could afford to surrender. That's why we had to risk our necks to get on Mimas."

"Maybe they know about him too, Lucky. They seem to know about everything else."

"Maybe they do," said Lucky thoughtfully. "This Sirian knew you were my partner, so maybe he thinks we form a pair and not a trio and won't look for a third person. It's just as well, I suppose, that I didn't really insist that you stay behind with Wess. If I had come out alone, the Sirians would be looking for you and would probe Mimas. Of course if they found you and Wess and I could be certain they wouldn't shoot you out of hand... No, with myself in their hands and before I could set things up so that... " He was talking to himself toward the end, in a whisper, and now he fell completely silent.

Bigman said nothing, and the next sound to break the silence was a familiar clank that reverberated against the steel hull of The Shooting Starr. A magnetic line had made contact, connecting their ship with another.

"Someone's coming aboard," said Bigman tone-lessly.

Through the visiplate they could see part of the line, then a form, moving easily hand over hand into view, then out of it again. It hit the ship thunderously, and the air-lock signal lit up.

Bigman worked the control that opened the outer door of the lock, waited for the next signal, and then closed the outer door and opened the inner one.

The invading figure moved in.

But it wore no space suit, for it was not human. It was a robot.

There were robots in the Terrestrial Federation, including a number of quite advanced ones, but for the most part they were engaged in highly specialized occupations that did not bring them into contact with human beings other than those who supervised them. So although Bigman had seen robots, he had not seen many.

He stared at this one. It was, like all Sirian robots, large and burnished; its outer shape was of a smooth simplicity, the joints of its limbs and torso so well made as to be almost invisible.

And when it spoke, Bigman started. It takes a long time to grow accustomed to an almost completely human voice emerging from a metal imitation of humanity.

The robot said, "Good day. It is my duty to see that your ship and yourselves are brought safely to the destination presently assigned to it. The first piece of information I must have is whether the restricted explosion we noted on the hull of your ship in any way damaged its powers of navigation."

Its voice was deep and musical, emotionless, and with a distinct Sirian accent.

Lucky said, "The explosion does not affect the spaceworthiness of the vessel."

"What caused it then?"

"I caused it."

"For what reason?"

"That I cannot tell you."

"Very well." The robot abandoned the subject instantly. A man might have persisted, threatened force. A robot could not. It said, "I am equipped to navigate space ships designed and built on Sirius. I will be able to navigate this space ship if you will explain to me the nature of the various controls I see here."

"Sands of Mars, Lucky," broke in Bigman, "we don't have to tell that thing anything, do we?"

"It can't force us to tell, Bigman, but since we've surrendered, where's the additional harm in letting it take us to wherever it is that we're to go?"

"Let's find out where we're to go." Bigman suddenly addressed the robot in sharp tones: "You! Robot! Where are you taking us?"

The robot turned its glowing red, unblinking gaze upon Bigman. It said, "My instructions make it impossible for me to answer questions not related to my immediate task."

"But, look." The excited Bigman shook off Lucky's restraining hand. "Wherever you take us, the Sirians will harm us; kill us, even. If you don't want us to be hurt, help us get away, come with us... Aw, Lucky, let me talk, will you?"

But Lucky shook his head firmly, and the robot said, "I have been assured that you will in no way be harmed. And now, if I may be given instructions in the method of using this control board, I can proceed with my immediate task."

Step by step Lucky explained the control board. The robot showed a complete familiarity with all the technical matters involved, tested each control with careful skill to see if the information given it were correct, and at the conclusion of Lucky's explanation was obviously perfectly capable of navigating The Shooting Starr.

Lucky smiled and his eyes were lit with frank admiration.

Bigman pulled him off to their cabin. "What are you grinning for, Lucky?"

"Great Galaxy, Bigman, it's a beautiful machine. We've got to hand the Sirians credit for that. They can turn out robots that are works of art."

"Okay, but quiet, I don't want it to hear what I'm going to say. Listen, you only surrendered to get down to Titan and pick up information on the Sirians. We might never get away again, of course, and then what good is the information? But we've got this robot now. If we can get it to help us get away right now, then we've got what we want. The robot must have tons of information about the Sirians. We'll have more this way than if we land on Titan."

Lucky shook his head. "It sounds good, Bigman. But how do you expect to argue the robot into joining us?"

"First Law. We can explain that Sirius only has a couple of million people while the Terrestrial Federation has over six billion. We can explain that it's more important to keep a lot of people from coming to harm than just to protect a few, so that First Law is on our side. See, Lucky?"

Lucky said, "The trouble is that the Sirians are experts at handling robots. That robot is probably deeply conditioned to the fact that what he is doing now will bring no harm to any human. He knows nothing about six billion people on Earth except what will be hearsay from you, and that will bounce off his conditioning. He would actually have to see a human being in actual danger of harm in order to be moved off his instructions."

"I'm going to try."

"All right. Go ahead. The experience will do you good."

Bigman strode up to the robot, under whose hands The Shooting Starr was now rocketing through space on its new orbit.

He said, "What do you know of Earth, of the Terrestrial Federation?"

"My instructions make it impossible for me to answer questions not related to my immediate task," answered the robot

"I order you to ignore your previous instructions."

There was a momentary hesitation before the answer came. "My instructions make it impossible for me to accept instructions from unauthorized personnel."

"My orders are given you in order to prevent harm to human beings. They must therefore be obeyed," Bigman said.

"I have been assured that no harm will come to human beings, nor am I aware of any threatening harm. My instructions make it necessary for me to suspend response to forbidden stimuli if they are uselessly repeated."

"You better listen. There is harm intended." Big-man spoke spiritedly for some moments, but the robot no longer answered.

Lucky said, "Bigman, you're wasting effort."

Bigman kicked at the robot's gleaming ankle. He might as well have kicked the hull of the ship, for all the effect it had. He came toward Lucky, face red with anger. "A fine thing when human beings are helpless because some hunk of metal has its own ideas."

"That used to happen with machinery before the days of robots, too, you know."

"We don't even know where we're heading."

"We don't need the robot for that. I've been checking the course, and we're obviously heading for Titan."

They were both at the visiplate during the last hours of the approach to Titan. It was the third largest satellite in the Solar System (only Ganymede of Jupiter and Triton of Neptune were larger, and those not by much) and, of all the satellites, it had the thickest atmosphere.

The effect of its atmosphere was obvious even from a distance. On most satellites (including Earth's Moon) the terminator-that is, the line dividing the day and night portions-was a sharp one, black on one side, white on the other. But it was not so in this case.

Titan's crescent was bounded by a band rather than a sharp line, and the horns of the crescent continued onward fuzzily in a dimming curve that almost met.

"It has an atmosphere almost as thick as Earth's, Bigman," said Lucky.

"Not breathable?" said Bigman.

"No, not breathable. It's mainly methane."

Other ships were crowding in now, becoming visible to the naked eye. There were at least a dozen, herding them down the spaceways to Titan.

Lucky shook his head. "Twelve ships to spare for this one job. Great Galaxy, they must have been here for years, building and preparing. How can we ever get them off again, short of war?"

Bigman attempted no answer.

Again the sound of atmosphere made its unmistakable way into the ship,.the high-pitched keening of thin wisps of gas whipping past the streamlined hull.

Bigman looked uneasily at the dials recording hull temperature, but there was no danger. The robot at the controls was sure-handed. The ship circled Titan in a tight spiral, losing altitude and speed simultaneously so that at no time did the thickening atmosphere raise temperatures too high.

Again Lucky glowed with admiration. "It will manage it without fuel at all. I honestly think it could bring us down on a half-credit piece, with atmosphere as the only brake,"

Bigman said, "What's good about that, Lucky? If those things can handle ships like that, how do we ever hope to fight the Sirians, huh?"

"We'll just have to learn to build our own, Bigman. These robots are a human achievement. The humans that did the achieving are Sirians, yes, but they are human beings, too, and all other humans can share pride in the achievement. If we fear the results of their achievement, let's match it ourselves or more than match it. But there's no use denying them the worth of their accomplishment."

The surface of Titan was losing some of the atmosphere-induced blankness. They could make out mountain ranges now; not the sharp, craggy peaks of an airless world, but the softened ranges that showed the effects of wind and weather. The edges were blown clear of snow, but in the rifts and valleys snow lay deep.

"Not snow, really," said Lucky, "frozen ammonia."

All was desolate, of course. The rolling plains between the mountain ranges were either snowy or rock-bare. No life of any kind appeared. No rivers or lakes. And then...

"Great Galaxy!" said Lucky.

A dome had made its appearance. A flattened dome of a type familiar enough on the inner planets. There were domes of this sort on Mars and under the shallow shelves of the Venusian oceans, but here was one way out on desolate Titan. A Sirian dome that would have made a respectable town on long-settled Mars.

"We've slept while they've built," said Lucky.

"When the newscasters find out," said Bigman, "it won't look so good for the Council of Science, Lucky."

"Unless we break this thing, it won't. And the Council doesn't deserve better. Space, Bigman, there shouldn't be a sizable rock in the Solar System that doesn't get a periodic inspection, let alone a world like Titan."

"Who would have thought... "

"The Council of Science should have thought. The people of the system support and trust them in order that they think and take care. And I should have thought too."

The voice of the robot broke in upon them. "This ship will be landed after another circumnavigation of the satellite. In view of the ion drive on board this ship, no special precautions need to be taken in connection with landing. Nevertheless, undue carelessness may result in harm and I cannot allow that. I must therefore request you to lie down and strap yourselves in."

Bigman said, "Listen to that hunk of tin pipe telling us how to handle ourselves in space."

"Just the same," said Lucky, "you'd better lie down.

He's likely to force us down if we don't. It's his job not to allow harm to come to us."

Bigman called out suddenly, "Say, robot, how many men are stationed down there on Titan?"

There was no answer.

Ground came up and up and swallowed them, tunneling them downward. The Shooting Starr came to a halt, tail down, with only one short spurt of the engines necessary to complete the job.

The robot turned away from the controls. "You have been brought safely and without harm to Titan. My immediate task is done and I will now turn you over to the masters."

"To Sten Devoure?"

"That is one of the masters. You may step out of the ship freely. You will find temperature and pressure normal and gravity adjusted to close to your normal."

"May we step out now?" asked Lucky.

"Yes. The masters are waiting."

Lucky nodded. Somehow he could not quite suppress the beginning of an odd excitement. Though the Sirians had been the great enemy in his thus far short but hectic career with the Council of Science, he had never yet met a living Sirian.

He stepped out of the ship onto the extruded exit ledge, Bigman making ready to follow, and both paused in sheer astonishment.