She nudged the trumpet-shaped lever. There was no sense of motion. 'It's not fast enough. It'll take an hour to get to the end and we've still got to go up to the top of the seep. How far below ground are we?'

He shrugged. 'More than a hundred spans, but less than two hundred.'

'That's another hour, probably two. Can we make it before we breathe all our air?'

'I don't know.'

'I'll have to go faster.'

'Go too fast and it may tear the construct apart.'

'Too slowly and it won't matter' she retorted.

The minutes ticked by. Occasionally they came up against an object that scraped along the skin of the construct. It was hot inside now.

'How hot is the tar in the Great Seep, Merryl?'

'I wouldn't know. It's warm on top, so it must be warmer inside.'

'Hot enough to cook us?'

'I couldn't say.'

'Do you think we're at the end of the tar tunnel yet?' Tiaan asked.

'Once the node failed, the walk of the tunnel would soon have gone liquid. We'd be in the swirl of the Great Seep right now.'

'We're too slow,' she fretted. And we're not going up. I've got to do something.'

She knew what to do but was reluctant to do it, since that would give away the secret of making thapters-constructs that could fly. But if they were going to die anyway …

'Could you have the prisoners blindfolded, please, Merry!7 And ask the slaves to turn their backs. I've got to do something to the construct and I don't want anyone to see.'

He went down. Tiaan unpacked the set of pink diamonds -powerful hedrons — and the strands of black whiskers, fifty-four of each, weighing them in her hands. So much from so little.

'It's done,' called Merryl.

She lowered herself down the ladder by her hands and Merryl caught her at the bottom. Tiaan exercised her legs at every opportunity but it was going to take weeks before she could walk properly.

Opening a hatch in the floor at the front, she identified a black box among the tangle of parts inside, and prised the lid off. Inserting the diamond hedrons into their sockets, she fed the black threads up to the back of the amplimet cavity, checking everything carefully as she worked. There would be no time to do it again.

As soon as it was done, Merryl lifted her up the ladder. How quickly she had come to rely on him. Tiaan took hold of the controls. The amplimet meshed with her snugly now, not opposing her at all. It wanted to escape as much as she did. The whine rose in pitch as she pulled up on the flight knob but nothing seemed to happen. She could not tell if they were moving upwards.

'Is it working, Merryl?'

He thought for a moment. 'You know how, when you carry a bowl of water, it moves with your motion?'

'Yes! What a clever idea.'

He found a broad metal dish among the bits and pieces in one ot the storage compartments, half filled it with water and sat it on the top of the binnacle. With a pointed instrument he scored marks around the dish, at the water level.

'That will show movement from side to side, or back and forth.'

'But not up, which is what I most need to know.' She wiped her brow. Sweat was running down her neck and her shirt was saturated. The air was getting stuffy, too.

'But if we had something springy …'

He was away half an hour of their precious time, before returning with thin strips of green material. 'I found a diaphragm in one of the drawers. It's a kind of rubber.'

Tying one strip from the ceiling, above the binnacle, Merryl knotted a small coin into the other end, one-handed. 'I've carried this copper nyd for twenty years,' he said with a hint of a smile, 'for luck — not that it's brought me any.' Merryl scored a line across the screen at the lowest edge of the coin and stood back. 'Try again.'

She moved the controller lever slightly. The water in the dish moved back a fraction. 'It works!' She gave him a triumphant grin, then a tentative hug. 'Let's try the other' Taking hold of the flying knob, she pulled it up. The rubbery strip lengthened perceptibly before oscillating around its original position.

'How fast do you think we're rising?' she said.

'Haven't a clue.'

She pulled the knob up further until the machine began to shudder, then backed it off a little. 'If we're only rising at a few spans an hour …I suppose it'll be an easy death, if we run out of air.'

He did not answer.

Tiaan settled back in her seat. 'How did the enemy come to capture you, Merryl?'

'We lost an unimportant little battle near Gosport, way over on the east coast; he said. 'We were fighting for a village you'd never have heard of. I don't remember its name. On the march we went through so many places that after a while no one could tell the difference.'

She wiped her dripping brow. Were you in the army a long time?'

'Only a few months. There was an emergency, and after a week of training we went to the front. I say 'the front", though there wasn't one. The lyrinx prefer to fight in small bands, or even alone. Most of my friends died in ambushes and isolated skirmishes. Afterwards, no one knew where; no one survived to write their Histories. The cursed war!'

There was a bang on the roof of the construct, followed by a scraping down the back.

'What was that?' said Tiaan.

'Something in the seep. Perhaps a piece of wood, or a large bone.' Merryl was staring straight ahead, as if to pierce the black tar.

'What did you do before you went into the army, Merryl?'

‘I was a translator, like my parents,' he said softly. 'But that's so long ago it doesn't seem like me at all. I can hardly imagine it now.'

They sat in silence, listening to the whine of the construct, the occasional thunk of some object or other striking the top of the machine, the creak and rattle of the metal skin. If we were going really slowly, she thought, the impacts wouldn't make any noise.

It grew hotter. Tiaan's clothes were sodden; Merryl's too. She could hear his hoarse breathing. Hers was the same. Surely they did not have much air left. Time seemed to be going very slowly.

'What about you, Tiaan? Tell me about yourself.’

She was equally reticent. 'There's not much to tell. I was chosen to become an artisan. I have a talent of thinking in pictures. I —’

Down below, someone groaned and began to thrash their legs. Merryl swung himself down the ladder. 'They're not looking good,' he called.

She poked her head down until she could see. Three of the seven slaves were asleep, or unconscious. The others sprawled limply on the floor, eyes closed, lungs heaving. Tirior and Minis were in better shape, though they looked worse than she felt. Nish lay curled up on a pull-out bunk, halfway up the wall. He had worked his blindfold off but his eyes were shut.

'The air's really bad down there,' Merryl said as he returned to her side. 'They won't last much longer.'

She pulled the knob up until the machine began to shudder. The rubber strip elongated. Everything began to vibrate, including her teeth. The construct squealed as if its metal carapace were being wrenched one way and then the other.

'I don't like the sound of that,' she said.

'Doesn't matter much, either way.'

'No.'

A while later she said, 'How fast now?' forgetting that she'd asked that before.

'I couldn't say, Tiaan.'

It was too much of an effort to talk. She leaned back against the seat, panting. Her head drooped.

The hatch above their heads squealed and a ribbon of tar jetted in from one side, festooning her arm and shoulder with coiling black bands. She tried to brush it off but the hot stuff stuck to her fingers and burned. Tiaan yelped and with her free hand pulled the flight knob down until the shuddering stopped.

Merryl tightened the hatch and sat on the floor, resting his head back against the wall. Tiaan set the controls and scraped the tar off. She felt so very tired; her head nodded. She hauled herself up, hanging onto the binnacle. If she sat down, she would go to sleep, which would swiftly be followed by unconsciousness, and death for everyone.