Tiaan sprang the walker backwards, colliding with the wall. She covered her face, peering through her fingers at Minis, and tears sprang to her eyes. She had invested all her foolish, youthful dreams in him, and he had cast her aside. She had to get away before he saw her. Whirling the walker around in its tracks she set off the other way, into her personal darkness. Towards the fire.

'Tiaan!' yelled Merryl.

She increased her speed, for his cry had given her away.

'Tiaan,' he yelled, pounding after her.

She could not move quickly in the gloom and Merryl caught her around the bend. 'Tiaan, what is it?'

'Those three are my enemies.'

He took her arm. 'You can't get out that way. Can't you smell the fumes?'

Just enough light came around the corner, now that her eyes had adjusted, to illuminate a dark, noxious cloud creeping along the floor. An odd tendril or two escaped upwards. One caught in the back of her throat and her lungs contracted.

All right,' she said hoarsely. 'But don't tell them my back has been repaired. Please.'

'I'll say nothing,' said Merryl. 'I know nothing.'

At the corner she almost ran into a racing Minis. 'Tiaan? Is it truly you?' He stopped abruptly, staring at the walker. His eyes lifted to her face. 'Tiaan,' he whispered. 'What happened?'

Her back was throbbing. She couldn't deal with Minis. All she could do was keep him at bay with words. 'My back was broken when the construct crashed,1 she said harshly. After your father attacked me without provocation.'

'I'm sorry. I tried to stop him …'

'Spare me your lies! I had enough of them in Tirthrax.' She ground the words out, then went past in silence. Tirior stared at her. Nish gaped. Tiaan did not acknowledge either of them.

In the open area, she said to Merryl, 'Is there any other way out?'

He pointed to the left, where another small tunnel yawned. 'It may be possible that way. If not, we're trapped and will die here.'

'Is the way the construct came in completely blocked?'

'It seems so.'

'Then we have no choice. Shall we scout this passage out?'

They had gone only a hundred paces up the small tunnel when they encountered a rivulet of molten tar oozing along the floor.

'I was afraid of that,' said Merryl. 'It seems we're doomed to end our lives here, Tiaan.'

Tiaan said nothing. They went back to the construct.

Tirior examined the walker shrewdly. 'An ingenious device. Did you make it?'

'What's the matter with your machine?' said Tiaan, ignoring the question.

'The node has gone dead and taken all the fields with it.' Tirior was watching Tiaan, head tipped to one side, no doubt wondering how the walker could still move. It would not take her long to work it out.

'Merryl' Tiaan said quietly. 'Order your people to take the Aachim, before they attack us.'

Tirior's hand darted for the pack she wore on her chest. Tiaan hurled the walker backwards, slamming painfully into the wall.

'Take them,' roared Merryl, throwing his handless arm across Tirior's throat and twisting her other arm up behind her back. The freed slaves did the same with Minis.

'Him as well' Tiaan shouted, pointing to Nish.

'You misjudge us' Tirior said softly, but under her breath she was muttering in an Aachim dialect Tiaan did not recognise.

Tiaan felt power flow from her controller and the walker's legs slowly splayed. Had Tirior not been exhausted from the mancery that had got her into Snizort, she might have succeeded.

'Stop her mouth!' Tiaan cried.

One of the slaves wound a strip of cloth three times around Tirior's head and pulled it tight. Tiaan felt the flow ease. Her heart was beating irregularly and she felt faint. So close.

'You taught me the value of your word, Tirior.' Tiaan wrenched open the pack, Tirior had been reaching for a small glass tube, capped in gold, with a scintillating powder inside. Tiaan tossed it into the tar and pressed it down with one of the walker's feet. 'Bind them, please. Merryl.'

Cord was found in a storeroom and the three prisoners' hands bound behind their backs.

'I'm not your enemy, Tiaan,' said Nish. I was wrong about you before. I'm sorry.'

He seemed different to the Nish Tiaan had known. He was more sure of himself, less angry, and made no attempt to fight those who held him. But Tiaan could not forgive so easily. 'Every time I've met you I've regretted it, Nish,' she said wearily.

'We were looking for you, to bring you out of here.'

Tiaan activated the walker and moved away. 'I have a plan,' she whispered to Merryl.

'I thought you must.'

'I think, with my crystal, that I may be able to operate the construct. If you can direct me to the way out, it will carry us through the fumes. For a while, at least.'

'I know every tunnel/ he said.

'Lift me into the construct and I'll see what I can do. The tar around it will have to be cleared away.'

'I'll have it done.'

Taking the amplimet from the walker, Tiaan put it in her pocket, undid the straps and lifted herself on her arms. Merryl carried her across. 'I'm not too heavy, am I?'

He smiled. 'You're no burden at all.'

He boosted her up the side and she slid her legs in. As her feet struck the floor Tiaan's knees buckled. Her muscles might have been made from cloth. Pulling out the operator's seat she sat down hurriedly.

The layout was much the same as in her thapter. She pressed the small recessed button and a hexagonal tube sprang out. Flipping the cap open, she removed the crystal, which was pale blue and striated down the sides. She had never seen one like it. Slipping it into her pocket, she put the amplimet in its place. In her own construct, or thapter as she had called it after learning how to make it fly, she'd made a special device to reduce power.

Tlaan hoped that would not he necessary here, since she was drawing from such a distant node. In any case, she had nothing to build it with.

She pressed the hexagonal tube in and closed the cap. After a long moment, a faint whine came from below, and a subtle tremor. It was working!

It took hours to remove the great gouts of sticky tar, and the work was so exhausting that the slaves had to rest after every few strokes. The job had just been completed when Merryl cried, Tiaan, look out!'

She got the hatch down just in time, as an even bigger clot buried the construct completely. By the time that had been removed, the air inside was stale. A day had gone by since her escape from the patterner.

The black miasma, which had advanced and retreated a number of times, was now flowing steadily across the floor. It would be up to their knees within minutes.

'Better bring the prisoners on board,' she said to Merryl, who was anxiously watching the fumes. Tiaan popped the amplimet out and pocketed it, just in case. There was no room for trust; the whole world seemed to be against her.

The prisoners were brought in and taken below. Minis gazed sorrowfully at her, like a dog that had been kicked. Nish, who looked as though he hadn't slept in days, simply lay down, pillowed his head on his arms and went to sleep. Tirior showed no expression at all. She was the one to watch.

Everyone came aboard save the two who were mattocking away at the sticky tar on the right-hand side. When the black fog was at the level of their thighs, Tiaan called them in. Should a sudden surge overwhelm the construct now, it would be impossible to get out.

Merryl set guards on the Aachim and Nish. The remaining slaves went below, leaving just her and Merryl in the operator's compartment. It would be very cramped down there, with nine passengers. Tiaan reinserted the amplimet and took hold of the trumpet-shaped lever. The whine rose in pitch but the construct did not move.

'It's still stuck in the tar,' said Merryl. ' I don't think —’