'Ah-hah!'

'I didn't mean—'

'Look, we're a lot further back in time than that,' said the Dean. 'Thousands of years, he says. No one's grandfather is alive.'

'That's a lucky escape for Mister Stibbons senior, then,' said Ridcully. 'No, sir,' said Ponder. 'Please! What I was trying to get across, sir, is that anything you do in the past changes the future. The tiniest little actions can have huge consequences. You might . . . tread on an ant now and it might entirely prevent someone from being born in the future!'

'Really?' said Ridcully. 'Yes, sir!' Ridcully brightened up. That's not a bad wheeze. There's one or two people history could do without. Any idea how we can find the right ants?'

'No, sir!' Ponder struggled to find a crack in his Archchancellor's brain into which could be inserted the crowbar of understanding, and for a few vain seconds thought he had found one. 'Because . . . the ant you tread on might be your own, sir!'

'You mean . . . I might tread on an ant and this'd affect history and I wouldn't be born?'

'Yes! Yes! That's it! That's right, sir!'

'How?' Ridcully looked puzzled. 'I'm not descended from ants.'

'Because . . .' Ponder felt the sea of mutual incomprehension rising around him, but he refused to drown. 'Well . . . er . . . well, supposing it . . . bit a man's horse, and he fell off, and he was carrying a very important message, and because he didn't get there in time there was a terrible battle, and one of your ancestors got killed – no, sorry, I mean didn't get killed—'

'How did this ant get across the sea?' said Ridcully. 'Clung to a piece of driftwood,' said the Dean promptly. 'It's amazing what can get even on to remote islands by clinging to driftwood, insects, lizards, even small mammals.'

'And then got up the beach and all the way to this battle?' said Ridcully. 'Bird's leg,' said the Dean. 'Read it in a book. Even fish eggs get transported from pond to pond on a bird's leg.'

'Pretty determined ant, then, really,' said Ridcully, stroking his beard. 'Still, I must admit stranger things have happened.'

'Practically every day,' said the Senior Wrangler. Ponder beamed. They had successfully negotiated an extended metaphor. 'Only one thing I don't understand, though,' Ridcully added. 'Who'll tread on the ant? 'What?'

'Well, it's obvious, isn't it?' said the Archchancellor. 'If I tread on this ant, then I won't exist. But if I don't exist, then I can't have done it, so I won't, so I will. See?' He prodded Ponder with a large, good-natured finger. 'You've got some brains, Mister Stibbons, but sometimes I wonder if you really try to apply logical thought to the subject in hand. Things that happen stay happened. It stands to reason. Oh, don't look so downcast,' he said, mistaking – possibly innocently – Ponder's expression of futile rage for shameful dismay. 'If you get stuck with any of this compl'cated stuff, my door's always open.[14] I am your Archchancellor, after all.'

'Excuse me, can we tread on ants or not?' said the Senior Wrangler peevishly. 'If you like.' Ridcully swelled with generosity. 'Because, in fact, history already depends on your treading on any ants that you happen to step on. Any ants you tread on, you've already trodden on, so if you do it again it'll be for the first time, because you're doing it now because you did it then. Which is also now.'

'Really?'

'Yes indeed.'

'So we should have worn bigger boots?' said the Bursar. 'Try to keep up, Bursar.' Ridcully stretched and yawned. 'Well, that seems to be it,' he said. 'Let's try to get back to sleep, shall we? It's been rather a long day.' Someone was keeping up. After the wizards got back to sleep, a faint light, like burning marsh gas, circled over them. He was an omnipresent god, although only in a small area. And he was omnicognizant, but just enough to know that while he did indeed know everything it wasn't the whole Everything, just the part of it that applied to his island. Damn! He'd told himself the cigarette tree would cause trouble. He should have stopped it the moment it started growing. He'd never meant it to get out of hand like this. Of course, it had been a shame about the other . . . pointy creature, but it hadn't been his fault, had it? Everything had to eat. Some of the things that were turning up on the island were surprising even him. And some of them never stayed stable for five minutes together. Even so, he allowed himself a little smirk of pride. Two hours between the one called the Dean dying for a smoke and the bush evolving, growing and fruiting its first nicotine-laden crop. That was evolution in action. Trouble was, now they'd start poking around and asking questions. The god, almost alone among gods, thought questions were a good thing. He was in fact committed to people questioning assumptions, throwing aside old superstitions, breaking the shackles of irrational prejudice and, in short, exercising the brains their god had given them, except of course they hadn't been given them by any god, lord knows, so what they really ought to do was exercise those brains developed over millennia in response to the external stimuli and the need to control those hands with their opposable thumbs, another damn good idea that he was very proud of. Or would have been, of course, if he existed.

However, there were limits. Freethinkers were fine people, but they shouldn't go around thinking just anything. The light vanished and reappeared, still circling, in the sacred cave on the mountain. Technically, he knew, it wasn't in fact sacred, since you needed believers to make a place sacred and this god didn't actually want believers. Usually, a god with no believers was as powerful as a feather in a hurricane, but for some reason he'd not been able to fathom he was able to function quite happily without them. It may have been because he believed so fervently in himself. Well, obviously not in himself, because belief in gods was irrational. But he did believe in what he did. He considered, rather guiltily, making a few more thunder lizards in the hope that they might eat the intruders before they got too nosey, but then dismissed the thought as being unworthy of a modern, forward-thinking deity. There were racks and racks of seeds in this part of the cave. He selected one from among the pumpkin family, and picked up his tools. These were unique. Absolutely no one else in the world had a screwdriver that small. A green shoot speared up from the forest litter in response to the first light of dawn, unfolded into two leaves, and went on growing. Down among the rich compost of fallen leaves, white shoots writhed like worms. This was no time for half-measures. Somewhere far down, a questing tap root found water. After a few minutes, the bushes around the by now large and moving plant began to wilt. The lead shoot dragged itself onwards, towards the sea. Tendrils just behind the advancing stem wound around handy branches. Larger trees were used as support, bushes were uprooted and tossed aside and a tap root sprouted to take possession of the newly vacated hole. The god hadn't had much time for sophistication. The plant's instructions had been put together from bits and pieces lying around, things he knew would work. At last the first shoot crossed the beach and reached the sea. Roots drove into the sand, leaves unfolded, and the plant sprouted one solitary female flower. Small male ones had already opened along the stem. The god hadn't programmed this bit. The whole problem with evolution, he'd told himself, was that it wouldn't obey orders. Sometimes, matter thinks for itself. A thin prehensile tendril bunched itself for a moment, then sprang up and lassoed a passing moth. It curved back, dipped the terrified insect waist deep in the pollen of a male flower, then coiled back with whiplash speed and slam-dunked it into the embracing petals of the female.

A few seconds later the flower dropped off and the small green ball below it began to swell, just as the horizon began to blush with the dawn. Argo nauticae uniquo was ready to produce its first, and only, fruit. There was a huge windmill, squeaking around on top of a metal tower. A sign attached to the tower read: 'Dijabringabeeralong: Check your Weapons.'

'Yep, still got all mine, no worries,' said Mad, urging the horses forward. They crossed a wooden bridge, although Rincewind couldn't see why anyone had bothered to build it. It seemed a lot of effort just to cross a stretch of dry sand. 'Sand?' said Mad. 'That's the Lassitude River, that is!' And, indeed, a small boat went past. It was being towed by a camel and was making quite good time on its four wide wheels. 'A boat,' said Rincewind. 'Never seen one before?'

'Not one being pedalled, no,' said Rincewind, as a tiny canoe went past. 'They'd hoist the sail if the wind was right.'

'But . . . this might sound a strange question . . . Why is it a boat shape?'

'It's the shape boats are.'

'Oh, right. I thought it'd be a good reason like that. How did the camels get here?' They cling to driftwood, people say. The currents wash a lot of stuff up, down on the coast.' Dijabringabeeralong was coming into view. It was just as well there had been the sign, otherwise they might have ridden through it without noticing. The architecture was what is known professionally as 'vernacular', a word used in another field to mean 'swearing' and this was quite appropriate. But then, Rincewind thought, it's as hot as hell and it never rains – all you need a house for is to mark some kind of boundary between inside and outside. 'You said this was a big town,' he said. 'It's got a whole street. And a pub.'

'Oh, that's a street, is it? And that logpile is a pub?'

'You'll like it. It's run by Crocodile.'

'Why do they call him Crocodile?'

A night sleeping on the sand hadn't helped the Faculty very much. And the Archchancellor didn't help even more. He was an early-morning man as well as being, most unfairly, a late- night man. Sometimes he went from one to the other without sleeping in between. 'Wake up, you fellows! Who's game for a brisk trot around the island? There'll be a small prize for the winner, eh?'

'Oh, my gods,' moaned the Dean, rolling over. 'He's doing press-ups.'

'I certainly wouldn't want anyone to think I'm advocating a return to the bad old days,' said the Chair of Indefinite Studies, trying to dislodge some sand from his ear, 'but once upon a time we used to kill wizards like him.'

'Yes, but we also used to kill wizards like us, Chair,' said the Dean. 'Remember what we'd say in those days?' said the Senior Wrangler. ' “Never trust a wizard over sixty-five”? Whatever happened?'

'We got past the age of sixty-five, Senior Wrangler.'

'Ah, yes. And it turned out that we were trustworthy after all.'

'Good thing we found out in time, eh?'

'There's a crab climbing that tree,' said the Lecturer in Recent Runes, who was lying on his back and staring straight upwards. 'An actual crab.'

'Yes,' said the Senior Wrangler. 'They're called Tree-climbing Crabs.'

'Why?'

'I had this book when I was a little lad,' said the Chair of Indefinite Studies. 'It was about this man who was shipwrecked on an island such as this and he thought he was all alone and then one day he found a footprint in the sand. There was a woodcut,' he added. 'One footprint?' said the Dean, sitting up, clutching his head. 'Well . . . yes, and when he saw it he knew that he—'

'—was alone on an island with a crazed one-legged long-jump champion?' said the Dean. He was feeling testy. 'Well, obviously he found some other footprints later on . . .'

'I wish I was on a desert island all alone,' said the Senior Wrangler gloomily, watching Ridcully running on the spot.

'Is it just me,' the Dean asked, 'or are we marooned thousands of miles and thousands of years from home?'

'Yes.'

'I thought so. Is there any breakfast?'