'Marco?' she said. He was hovering some way off, still wrapped in self-recrimination.

There was a sigh in her ear. 'I can hold no useful opinions,' he said, 'but I see no obvious dangers.'

The island was small and obviously tidal. Seaweed, now almost dry, covered most of it. So many fires had been lit at the highest point of the rock, about three metres above the sea now, that it was black.

Kin landed first, and keeled over as her legs refused to support her. A crab scuttled out of the seaweed in front of her face.

Silver landed lightly and then hauled on the line to tow the dumbwaiter out of the sky. While Kin sat massaging some life back into her legs the shand bustled round cutting seaweed for the machine's intake hopper. In normal use the dumbwaiter extracted all its molecules from the air around it, but Silver had a big appetite.

After a while she tapped Kin on the shoulder and handed her a cup of coffee, reserving a large bowl of something red for herself. It was quite possibly synthetic shand. So what?

'Where's Marco?' said Kin, looking round. Silver swallowed and pointed upward.

'He's switched off his transmitter,' she said. 'He has problems, that one.'

'You're not kidding,' said Kin. 'He thinks he's a human and knows he's a kung. And every time he acts like a kung he feels ashamed.'

'All kung and humans are crazy,' said Silver conversationally. 'He's craziest. If he thought about it he would realize there's a logical impossibility about all this.'

'Oh, yes,' said Kin wearily. 'I know he's not physically human, but the kung believe one's being is determined by the place--' She stopped. Silver was grinning encouragingly, and nodding.

'Go on,' she said. 'You're nearly there. Kung think the nearest available soul enters the offspring at birth. But Marco is supposed to be human. Humans don't really believe that kind of superstition, do they? Ergo, he must be a body-and-soul kung.'

There was a gasp in Kin's ear. Marco may have switched off his transmitter, but kung were paranoid. He'd never switch off his receiver. Kin looked up at the distant dot in the air. Silver mouthed the words: ignore him.

'I suppose Leiv's people lit those fires,' said Kin vaguely. 'We must be on a trade route.'

'Yes. Have you noticed the variations in the sea's roughness?'

Kin had.

There were billions of tons of water on the disc, constantly draining over the edge. It had to get back somehow. Assuming the disc builders couldn't work magic, there was a molecule sieve down there, connected to -- Kin writhed -- a matter transmitter. Simple. You clamp receivers to the sea floor and pump the water back, only things were going wrong.

Over the last day and a half they had passed over circular areas of raging sea. Too much was coming up, or maybe only a few receivers were still available to take the volume.

'I keep forgetting this is just a big machine,' she said.

'I think you are being too hard on the disc builders,' said Silver. 'Apart, of course, from the possibilities of a breakdown, there is no great disadvantage to living in a cosmos like this, surely? You can still evolve a science.'

'Sure. The wrong science. Science is supposed to be the tool with which you can unscrew the universe, but disc science is only fit for the disc. It'd be closed, stagnant. Try to imagine a sophisticated disc astronomer trying to figure our sort of universe! The disc is only good for religions.'

Silver dialled herself another bowl of goo. When she looked back Kin was shrugging out of her suit.

'Do you think that is wise?'

'Almost certainly not,' said Kin, swaying slightly as a swell caught them. 'But I'm damned if I'm going to sweat in there all day long. I'd give a handful of Days for a hot bath.'

She walked naked towards the water and stopped abruptly as another swell nearly made her miss her footing.

On an island?

Marco dived out of the sky, screaming in kung. A wave washed over Kin's feet, and as she turned the next one came in waist high and knocked her over. Through stinging spray she saw Silver and the dumbwaiter rocket out of the surf.

Cold water rolled over her. She groped in the green, ear-blocking light and managed to grab the fabric of the suit. It dragged at her as the dead weight of the lift belt pulled it down.

Beside her the water exploded into bubbles. Marco thrashed past, and there was a horrible moment before the suit pulled again -- upwards.

Silver was waiting. As the suit came up with Kin gripping it desperately she drifted closer. Marco surfaced in a rosette of foam.

'No!' he screamed. 'Height! Get height! We're too near the sea!'

The grim pantomime started again 200 metres up. With Silver holding Kin by the shoulders and Marco arranging the suit, they managed to slot her into the lower section, then forced her freezing arms into the sleeves. The inner thermal suit clicked on; by the time Kin was fit to talk the inside of the suit was a Turkish bath.

'Thanks, Marco,' she said. 'You know, I never would have had the intelligence to switch--'

'Look below,' said the kung.

They looked.

A shadow moved under the sunlit waves, a big turtle, island sized, with four paddle legs and a head the size of a small house. As they watched it flapped lazily into the depths.

'I saw it wake,' said Marco. 'I had been pondering the regularity of the legs, wondering if they were shoals, and then one moved. No doubt it makes a practice of this and feeds on the unfortunates who light fires on its shell.'

'A carapace length of a hundred metres,' mused Silver. 'Remarkable. Do such exist on Earth, Kin?'

'No,' said Kin, through chattering teeth.

'Enough of this scientific chit-chat,' said Marco. 'We must make speed for the nearest land mass. Silver, will you look yonder? About out-by-right, middle heaven. I only see a dot.'

Silver turned her suit.

'It's a bird,' she said. 'Black. Possibly a raven.'

'Then at least we cannot be far from land,' said Marco. 'I was afraid it was a dragon.'

They switched the belts to maximum horizontal motion and headed on. Imperceptibly Marco pulled ahead, so that they travelled in delta formation. Kin assisted by slowing her suit fractionally, and noticed that Silver had done the same. Marco the kung was in command.

After a while he started to climb, the others following obediently. Below...

... the disc unfolded. At their old height Kin could have believed they were on a globe, but now the disc spread out below them for what it was -- a lunatic map, a madman's Great Circle projection.

Cloud and the opacity of the air were the only barriers to vision. Kin could see the far rim of the disc, a darker line against the sky, and from that distant confusion of earth and sky two white horns grew and spread outward. The waterfall. The oceanfall, encircling the disc like a snake.

There was a hurricane building up, off the coast of Africa. As Kin climbed she watched the frozen spiral of cloud, fascinated.

She had seen worlds from space, but the disc was different. And it was big. She was used to thinking in terms of millions and the disc, spinning through space inside its own private universe, had sounded small. Seen from a few hundred miles up it was huge, real. It was the light-years of nothingness that were small and meaningless. It was enough now just to stare...

'Note the circles of disturbance in the ocean,' said Marco.

'Kin suggests there is something the matter with the mechanism that recirculates the sea water,' said Silver. 'Logical. Certainly I feel increased admiration for a people who face all this in small boats, with no air support.'

Silver said, 'Seeing the disc like this, one feels one would be nervous of setting foot on it again. It is too thin, too artificial. We do not as a rule suffer from vertigo, but seeing the disc like this I begin to comprehend what it means.'