Teppic stared at the line in the rock. Geometry. That was it. 'We'll go to Ephebe,' he said. 'They know all about geometry and they have some very unsound ideas. Unsound ideas are what I could do with right now.'

'Why do you carry all these knives and things? I mean, really?'

'Hmm? Sorry?'

'All these knives. Why?'

Teppic thought about it. 'I suppose I don't feel properly dressed without them,' he said.

'Oh.'

Ptraci dutifully cast around for a new topic of conversation. Introducing Topics of Amusing Discourse was also part of a handmaiden's duties. She'd never been particularly good at it. The other girls had come up with an astonishing assortment: everything from the mating habits of crocodiles to speculation about life in the netherworld. She'd found it heavy going after talking about the weather.

'So,' she said. 'You've killed a lot of people, I expect?'

'Mm?'

'As an assassin, I mean. You get paid to kill people. Have you killed lots? Do you know you tense your back muscles a lot?'

'I don't think I ought to talk about it,' he said.

'I ought to know. If we've got to cross the desert together and everything. More than a hundred?'

'Good heavens, no.,

'Well, less than fifty?'

Teppic rolled over.

'Look, even the most famous assassins never killed more than thirty people in all their lives,' he said.

'Less than twenty, then?'

'Yes.'

'Less than ten?'

'I think,' said Teppic, 'it would be best to say a number between zero and ten.'

'Just so long as I know. These things are important.' They strolled back to You Bastard. But now it was Teppic who seemed to have something on his mind.

'All this senate . . .' he said.

'Congress,' corrected Ptraci.

'You . . . er . . . more than fifty people?'

'There's a different name for that sort of woman,' said Ptraci, but without much rancour.

'Sorry. Less than ten?'

'Let's say,' said Ptraci, 'a number between zero and ten.' You Bastard spat. Twenty feet away the blowfly was picked cleanly out of the air and glued to the rock behind it.

'Amazing how they do it, isn't it,' said Teppic. 'Animal instinct, I suppose.'

You Bastard gave him a haughty glare from under his sweep-the-desert eyelashes and thought:

. . . Let z=ei0. cudcudcud Then dz=ie[i0]d0=izd0 or d0=dz/iz . . .

Ptaclusp, still in his nightshirt, wandered aimlessly among the wreckage at the foot of the pyramid.

It was humming like a turbine. Ptaclusp didn't know why, knew nothing about the vast expenditure of power that had twisted the dimensions by ninety degrees and was holding them there against terrible pressures, but at least the disturbing temporal changes seemed to have stopped. There were fewer sons around than there used to be; in truth, he could have done with finding one or two.

First he found the capstone, which had shattered, its electrum sheathing peeling away. In its descent from the pyramid it had hit the statue of Hat the Vulture-Headed God, bending it double and giving it an expression of mild surprise.

A faint groan sent him tugging at the wreckage of a tent. He tore at the heavy canvas and unearthed IIb, who blinked at him in the grey light.

'It didn't work, dad!' he moaned. 'We'd almost got it up there, and then the whole thing just sort of twisted!'

The builder lifted a spar off his son's legs.

'Anything broken?' he said quietly.

'Just bruised, I think.' The young architect sat up, wincing, and craned to see around.

'Where's Two-ay?' he said. 'He was higher up than me, nearly on the top-'

'I've found him,' said Ptaclusp.

Architects are not known for their attention to subtle shades of meaning, but IIb heard the lead in his father's voice.

'He's not dead, is he?' he whispered.

'I don't think so. I'm not sure. He's alive. But. He's moving - he's moving . . . well, you better come and see. I think something quantum has happened to him.'

You Bastard plodded onwards at about 1.247 metres per second, working out complex conjugate co-ordinates to stave off boredom while his huge, plate-like feet crunched on the sand.

Lack of fingers was another big spur to the development of camel intellect. Human mathematical development had always been held back by everyone's instinctive tendency, when faced with something really complex in the way of triform polynomials or parametric differentials, to count fingers. Camels started from the word go by counting numbers.

Deserts were a great help, too. There aren't many distractions. As far as camels were concerned, the way to mighty intellectual development was to have nothing much to do and nothing to do it with.

He reached the crest of the dune, gazed with approval over the rolling sands ahead of him, and began to think in logarithms.

'What's Ephebe like?' said Ptraci.

'I've never been there. Apparently it's ruled by a Tyrant.'

'I hope we don't meet him, then.'

Teppic shook his head. 'It's not like that,' he said. 'They have a new Tyrant every five years and they'do something to him first.' He hesitated. 'I think they ee-lect him.'

'Is that something like they do to tomcats and bulls and things?'

'Er.'

'You know. To make them stop fighting and be more peaceful.'

Teppic winced. 'To be honest, I'm not sure,' he said. 'But I don't think so. They've got something they do it with, I think it's called a mocracy, and it means everyone in the whole country can say who the new Tyrant is. One man, one-' He paused. The political history lesson seemed a very long while ago, and had introduced concepts never heard of in Djelibeybi or in Ankh-Morpork, for that matter. He had a stab at it, anyway. 'One man, one vet.'

'That's for the eelecting, then?'

He shrugged. It might be, for all he knew. 'The point is, though, that everyone can do it. They're very proud of it. Everyone has-' he hesitated again, certain now that things were amiss - 'the vet. Except for women, of course. And children. And criminals. And slaves. And stupid people. And people of foreign extraction. And people disapproved of for, er, various reasons. And lots of other people. But everyone apart from them. It's a very enlightened civilisation.'

Ptraci gave this some consideration.

'And that's a mocracy, is it?'

'They invented it in Ephebe, you know,' said Teppic, feeling obscurely that he ought to defend it.

'I bet they had trouble exporting it,' said Ptraci firmly.

The sun wasn't just a ball of flaming dung pushed across the sky by a giant beetle. It was also a boat. It depended on how you looked at it.

The light was wrong. It had a flat quality, like water left in a glass for weeks. There was no joy to it. It illuminated, but without life; like bright moonlight rather than the light of day.

But Ptaclusp was more worried about his son.

'Do you know what's wrong with him?' he said.

His other son bit his stylus miserably. His hand was hurting. He'd tried to touch his brother, and the crackling shock had taken the skin off his fingers.

'I might,' he ventured.

'Can you cure it?'

'I don't think so.'

'What is it, then?'

'Well, dad. When we were up on the pyramid . . . well, when it couldn't flare . . . you see, I'm sure it twisted around . . . time, you see, is just another dimension . . . um.'

Ptaclusp rolled his eyes. 'None of that architect's talk, boy,' he said. 'What's wrong with him?'

'I think he's dimensionally maladjusted, dad. Time and space has got a bit mixed up for him. That's why he's moving sideways all the time.'

Ptaclusp IIb gave his father a brave little smile.

'He always used to move sideways,' said Ptaclusp. His son sighed. 'Yes, dad,' he said. 'But that was just normal. All accountants move like that. Now he's moving sideways because that's like, well, it's like Time to him.' Ptaclusp frowned. Drifting gently sideways wasn't IIa's only problem. He was also flat. Not flat like a card, with a front, back and edge - but flat from any direction.

'Puts me exactly in mind of them people in the frescoes,' he said. 'Where's his depth, or whatever you call it?'

'I think that's in Time,' said IIb, helplessly. 'Ours, not his.'

Ptaclusp walked around his son, noting how the flatness followed him. He scratched his chin.

'So he can walk in Time, can he?' he said slowly.

'That may be possible, yes.'

'Do you think we could persuade him to stroll back a few months and tell us not to build that bloody pyramid?'

'He can't communicate, dad.'

'Not much change there, then.' Ptaclusp sat down on the rubble, his head in his hands. It had come to this. One son normal and stupid, one flat as a shadow. And what sort of life could the poor flat kid have? He'd go through life being used to open locks, clean the ice off windscreens, and sleeping cheaply in trouser-presses in hotel bedrooms[24]. Being able to get under doors and read books without opening them would not be much of a compensation. IIa drifted sideways, a flat cut-out on the landscape.

'Can't we do anything?' he said. 'Roll him up neatly, or something?'

IIb shrugged. 'We could put something in the way. That might be a good idea. It would stop anything worse happening to him because it, er, wouldn't have time to happen in. I think.'

They pushed the bent statue of Hat the Vulture-Headed God into the flat one's path. After a minute or two his gentle sideways drift brought him up against it. There was a fat blue spark that melted part of the statue, but the movement stopped.

'Why the sparks?' said Ptaclusp.

'It's a bit like flarelight, I think.'

Ptaclusp hadn't got where he was today - no, he'd have to correct himself - hadn't got to where he had been last night without eventually seeing the advantages in the Unlikeliest situations.

'He'll save on clothing,' he said slowly. 'I mean, he can just paint it on.'

'I don't think you've quite got the idea, dad,' said IIb wearily. He sat down beside his father and stared across the river to the palace.

'Something going on over there,' said Ptaclusp. 'Do you think they've noticed the pyramid?'

'I shouldn't be surprised. It's moved around ninety degrees, after all.'

Ptaclusp looked over his shoulder, and nodded slowly.

'Funny, that,' he said. 'Bit of structural instability there.'

'Dad, it's a pyramid! We should have flared it! I told you! The forces involved, well, it's just too-'

A shadow fell across them. They looked around. They looked up. They looked up a bit more.

'Oh, my,' said Ptaclusp. 'It's Hat, the Vulture-Headed God...'

Ephebe lay beyond them, a classical poem of white marble lazing around its rock on a bay of brilliant blue-

'What's that?' said Ptraci, after studying it critically for some time.

'It's the sea,' said Teppic. 'I told you, remember. Waves and things.'

'You said it was all green and rough.'

'Sometimes it is.'

'Hmm.' The tone of voice suggested that she disapproved of the sea but, before she could explain why, they heard the sound of voices raised in anger. They were coming from behind a nearby sand dune.

There was a notice on the dune.

It said, in several languages: AXIOM TESTING STATION.

Below it, in slightly smaller writing, it added: CAUTION - UNRESOLVED POSTULATES.

As they read it, or at least as Teppic read it and Ptraci didn't, there was a twang from behind the dune, followed by a click, followed by an arrow zipping overhead. You Bastard glanced up at it briefly and then turned his head and stared fixedly at a very small area of sand.

A second later the arrow thudded into it.

Then he tested the weight on his feet and did a small calculation which revealed that two people had been subtracted from his back. Further summation indicated that they had been added to the dune.