Silver chewed on another mouthful of what, Marco presumed, was lightly cooked shand.

'It seems remarkably remiss of the disc builders to allow this dereliction,' she said. 'I have noticed quite a number of obviously broken-down devices. Surely they could be repaired?'

'Who repairs the machines that do the repairing?' said Marco. 'A machine like the disc must blow a whole lot of fuses in a hundred years or so. What do you do when the robot that repairs the machines that make the parts for the factory that builds the robots that service the waldoes that make the fuses crashes its cog? Unless you get periodic servicing from outside, the disc gradually breaks down.'

'We could ask the robot,' said Silver.

It was a sick joke. The robot would answer any direct question about the mechanical scenery -- they had been treated to a ten-minute lecture on the tide regulation machinery, for example -- but ignored all the others. Marco had toyed with the idea of prising its lid off with something, but allowed caution to get the better of him.

'The place with the red lights must have been out near the disc rim,' said Silver. 'I have a feeling we're approaching the hub again. Perhaps we can ask Kin.'

The robot, which had been sitting silently a few metres away, rolled forward.

'We are refreshed?' it asked cheerfully. 'We will proceed?'

They stood up stiffly. The cuboid robot led them along a catwalk that opened on to a wide circular gallery, brilliantly lit. Most of the light came from the luminous mist overhead, but an appreciable amount came from the tiny actinic sun.

It floated perhaps a hundred metres over a perfect relief model of the disc surface, several hundred metres across. Except that relief maps didn't have tiny clouds, trailing minute shadows across the land. Marco had never seen them with active volcanoes, either.

There was no railing to the gallery. The disc-map glittered a metre below it, sunlight glinting off seas that looked disconcertingly real.

Marco stared down for a long time. Then he said, 'I give up. It's beautiful. What's it for?'

'One thinks of architect's models,' rumbled Silver. 'However, let me draw your attention to a flaw. See over there, just beyond the inland sea?'

Marco squinted, and gave up. 'No' he said. "The disc builders either had damn good eyesight or all this was just for show.'

He looked around for the robot. It wasn't there.

'We wish to view the disc map more closely,' Silver was saying to the empty air. Something like a flying slab of glass glided around the map from the far side and hovered in front of her. She stepped aboard gingerly. Under her weight it didn't even wobble.

'I see it,' said Marco, 'but I don't believe it. How did you do it?'

'Just a knack,' said Silver. 'I think I'm getting to understand the way things work around here. Coming?'

The glass carpet responded neatly to Silver's spoken directions. It skimmed across the map mere centimetres from the clouds. Marco had a strange urge to reach down and stir some into a cyclone. The map was frighteningly real. If he leaned over and touched it, would a giant hand appear in the disc sky?

When the shand spoke again he looked down obediently through the glass.

There was scarred land down there, burned and broken. And in the centre of it was a neat round hole.

Later Silver found that raising the platform slightly magnified the scene immediately beneath. There appeared to be no limit to the resolving power. There were people down there, microscopic figures that were almost immobile.

Only almost. Every second the scene flickered, and the figures took up slightly different positions. Marco spent an age entranced at the sight of a homunculus cutting wood. Flick -- the axe in the air -- flick -- biting into the tree -- flick -- back in the air; and a wedge of raw wood bitten by magic out of the trunk.

'It could be done' he said, half to himself. 'All you'd have to do is correlate sensory inputs and keep reprojecting them as a hologram.'

'You'd need many inputs.'

'Billions. You'd have to plug into the cognitive centre of every living creature.'

'Have you noticed the blank patches?'

'Maybe a bird wasn't looking in that direction at the time.'

Silver nodded gravely, and looked around the big map hall.

'Presumably the map of the disc also includes its own miniature disc map' she said slowly. She met Marco's gaze with a quiet smile. Then she ordered the platform to go to the map's hub. Neither doubted that the map hall was at the hub.

They looked down at the dome. Silver tried some commands, which appeared to have no effect. So she lowered the platform.

Staring down between their feet they saw earth and metal melt and drift aside. Disc machinery rose and faded away. There was something now, the edge of something...

There was a little round disc. At its centre was a grey and white speck, which resolved into two figures. One was big and furry, the other wiry and thin as a twig. Both were staring intently at something between their feet...

Flick. The wiry one was looking up now, at the miniature gallery that encircled the map of the map. Flick. There was a figure there. Flick. It raised a hand. Flick.

'Hi' said Kin.

Silver was not expert in human expressions, but by the look of her the woman had not been sleeping. In fact she was swaying slightly.

'Glad you could make it' she said. 'I couldn't get the computers to teleport you, there's a thirty per cent chance the power would fail while you were out of phase. Follow me. There isn't a lot of time left.'

'We--' began Marco.

Kin shook her head violently. 'No we didn't' she said. 'Come on!'

The kung started to protest again, and Silver gripped him firmly by a couple of arms. Kin was already hurrying down a tunnel leading off the hall.

It emerged in a metal cave half as big again as the one they had just left. It contained a spacecraft. At least, that was the first impression...

It didn't have any motors. Apart from strangely large altitude jets in about the right places for altitude jets, the hull seemed to be all cabin, with enough windows to grow grapes. Cuboid robots were still clustered around it. One of them was spraying paint on the landing gear. Two others were busy on a stubby wing.

Kin was already aboard. Snarling, Marco bounded up the short ladder and saw her sitting at the horseshoe-shaped instrument console. Wires trailed away from it to boxes bolted haphazardly around the interior of the cabin. In the centre of the floor a regiment of tiny cubes were engaged in feverish activity around a tangle of wires and metal shapes. One of them butted Marco politely on the foot until he moved.

'Silver, shut that door' said Kin. 'Hurry! And now pray to any convenient gods.'

She turned and addressed the air, in a tone of voice that made it clear it was not the others she was talking to.

'We're ready.'

The reply came from everywhere.

WE HAVE A BARGAIN?

It's a bargain' said Kin. There was a pause. The ship trembled slightly. Marco looked out and saw the cave walls slipping past.

'Don't say anything rash' said Kin. 'Don't even think, if you want to get home. Have a little faith, will you? Please?'

Sudden sunlight filled the cabin. Looking up, Marco and Silver saw a square of golden sky appear as sections of the roof slid back. The ship accelerated upwards on its section of floor.

By their feet a small robot tugged a length of tubing out of the heap in the centre of the cabin. One of its many arms swung down, hesitated, gripped the tube. The metal broke where it touched.

Silver jerked her head forward sharply as something tickled her ears. When she looked round cautiously she was eyeball to scanner with a little metal cube which was hanging from the cabin roof by three arms. It had no face, but managed to look embarrassed. Its fourth arm held a pair of calipers.