Ptraci's brows furrowed. 'Who reigns nearly every day?' she said.

'No, I mean rain. You know. Very thin water coming out of the sky?'

'What a silly idea. Where do you come from?'

Teppic looked miserable. 'Where I come from is Ankh-Morpork. Where I started from is here.' He stared down the track. From here, if you knew what you were looking for, you could just see a faint crack running across the rocks. It climbed the cliffs on either side, a new vertical fault the thickness of a line that just happened to contain a complete river kingdom and 7,000 years of history.

He'd hated every minute of his time there. And now it had shut him out. And now, because he couldn't, he wanted to go back.

He wandered down to it and put his hand over one eye. If you jerked your head just right . . .

It flashed past his vision briefly, and was gone. He tried a few times more, and couldn't see it again.

If I hacked the rocks away? No, he thought, that's silly. It's a line. You can't get into a line. A line has no thickness. Well known fact of geometry.

He heard Ptraci come up behind him, and the next moment her hands were on his neck. For a second he wondered how she knew the Catharti Death Grip, and then her fingers were gently massaging his muscles, stresses melting under their expert caress like fat under a hot knife. He shivered as the tension relaxed.

'That's nice,' he said.

'We're trained for it. Your tendons are knotted up like ping— pong balls on a string,' said Ptraci.

Teppic gratefully subsided on to one of the boulders that littered the base of the cliff and let the rhythm of her fingers unwind the problems of the night.

'I don't know what to do,' he murmured. 'That feels good.'

'It's not all peeling grapes, being a handmaiden,' said Ptraci. 'The first lesson we learn is, when the master has had a long hard day it is not the best time to suggest the Congress of the Fox and the Persimmon. Who says you have to do anything?'

'I feel responsible.' Teppic shifted position like a cat.

'If you know where there is a dulcimer I could play you something soothing,' said Ptraci. 'I've got as far as «Goblins Picnic» in Book I.'

'I mean, a king shouldn't let his kingdom just vanish like that.'

'All the other girls can do chords and everything,' said Ptraci wistfully, massaging his shoulders. 'But the old king always said he'd rather hear me. He said it used to cheer him up.'

'I mean, it'll be called the Lost Kingdom,' said Teppic drowsily. 'How will I feel then, I ask you?'

'He said he liked my singing, too. Everyone else said it sounded like a flock of vultures who've just found a dead donkey.'

'I mean, king of a Lost Kingdom. It'd be dreadful. I've got to get it back.'

You Bastard slowly turned his massive head to follow the flight of an errant blowfly; deep in his brain little columns of red numbers flickered, detailing vectors and speed and elevation. The conversation of human beings seldom interested him, but it crossed his mind that the males and females always got along best when neither actually listened fully to what the other one was saying. It was much simpler with camels.

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.