Something struck the construct hard, sending a shiver through the bowl of water. The hatch scraped as if the machine were sliding along the underside of something large and hard.

Tiaan could not think clearly. She pushed the controller forwards, the squeal became a shriek of tormented metal then, to her horror, the hatch was prised up a finger's width and thick tar began to ribbon in.

The noise stopped. They were free of the obstruction. Tiaan tilted the front of the construct up. The bowl of water slid off the binnacle, pouring its contents down the ladder. Pulling the flight knob up as far as it would go, she prayed.

The machine shuddered, the tar boiled beneath it and with a roar the construct hurled itself vertically. A surge of hot tar coated the wall at her back. The sound was indescribable. Tiaan felt sure the machine was going to tear itself apart.

Then the shuddering ceased, so abruptly that she did not understand what had happened. Had they stopped? No, for the mechanism down below was still screaming. She'd done it. The construct was free, in the open air, and going up like a skyrocket.

Tiaan threw open the hatch and, gasping lungfuls of sweet, pure air, let the machine fly where it would. There were groans and cries as the passengers were flung from one side to the other, but they were alive, at least. She did not look down. Tiaan had strength only to cling to the side, her eyes watering in the gale that swirled in through the jagged hatchway.

It became bitterly cold and hard to breathe; she'd gone too high. Tiaan eased the flight knob down, wondering where to go, but the whine broke for a second. As she levelled out it broke again and smoke belched up on all sides. She put the front down, heading towards the ground. Had something vital been damaged in all that shaking and shuddering? If the mechanism failed at this height they would be smashed to jelly.

There were no more problems until, nearing the ground, she levelled out and the whine faded to nothing. An acrid smell drifted from behind the binnacle and a long black trail smoked in the air behind them. Perhaps she'd drawn too much power and the workings were burning out.

To her right stood the main encampment of the human armies, their command post perched on a flat-topped hill. A little closer to her left, Tiaan glimpsed the seven-sided command area of the Aachim, next to thousands of motionless constructs. She wasn't going that way.

White fumes came up the steps from the lower level. Merryl cried out something she could not hear. There were yells and screams from below.

'Tiaan,' Merryl yelled. 'We're on fire! Put it down, anywhere!

Better that humanity have the secret of flight than that the Aachim get it. She cut the power and turned right, skimming across the brown grass. The whine failed. The construct hit the ground, bounced like a stone on water, bounced again and skidded around in a circle, before thumping into a rock and toppling on its side.

Tiaan hit her head, hard enough to daze her. She hung onto the binnacle, gasping, as the people below scrambled for the ladder.

'Get out!' screamed Merryl.

Tiaan hit the release, snatched the amplimet and pulled herself out through the torn and tarry hatch, tumbling a short distance to the muddy ground. The underside of the construct must have been red hot — she could feel the heat from here because the brown grass began to smoulder, then burst into flame.

Two people emerged from the hatch, coughing so hard that they doubled over. They were freed slaves; Tiaan did not know their names. After them came Tirior, still bound and gagged, two more slaves, then Minis, dragging the fifth. Nish, whose hands were free, crawled out last. He untied Tirior and they hauled the others away from the fire. The burning grass was expanding away from the other side of the construct, which was now enveloped in flames and smoke. Where was Merryl?

White smoke puffed through the hatch. Tiaan thought she saw a shadow move inside. 'Merryl!' she yelled.

She dragged herself back to the hatch and sat up, stretching out her useless legs. The sixth slave lay unconscious in the hatchway. Merryl was behind her, pushing ineffectually.

Seizing the woman by the front of her shirt, Tiaan pulled her out and they fell together on the grass. Merryl flopped beside Tiaan, coughing so hard she could see specks of blood on his tongue.

'The grass is burning,' Tiaan said. 'We've got to get away from here.'

Tirior wrenched her gag off before carrying the unconscious slave to safety.

Merryl stood up, his eyes watering. 'I'm all right,' he said hoarsely. He picked Tiaan up and lurched away.

As they emerged from behind the construct, Tiaan saw a squad of soldiers racing down from the human command area. Behind them were uniformed officers, as well as shadowy figures in robes — the scrutators.

To her left, and closer, a small band of Aachim were sprinting towards her, Vithis at their head. Even from this distance she could see the angry set of his face. Tiaan let out an involuntary gasp.

'What's the matter?' said Merryl.

'That Aachim is my worst enemy.'

'Then he mustn't get you.'

He began to stagger the other way, towards the human lines. Tiaan looked over her shoulder. It would be a close thing. They went by Minis, who had freed his hands. He stared at Tiaan as she passed, his eyes tragic black holes.

'Minis!' roared Vithis, his robes flapping. 'You're alive!'

'Yes, Foster-father, I am.'

'Stop her!'

Minis, who looked as if he was about to cry, said, 'Foster-father, I will not,' and threw himself face-down on the grass.

Merryl kept going, lurching blindly from side to side. His red eyes were streaming. He looked around wildly then ran, not for the human camp but back towards Snizort.

'Merryl,' cried Tiaan, 'you're going the wrong way.'

He turned around, his eyes watering so badly that everything must have been a blur. Vithis was racing towards them but the scrutators were going to get there first.

In the confusion of the moment, Nish must have thought that Merryl was trying to carry Tiaan off. He roared, 'You're not taking her anywhere!' and launched himself through the air. His shoulder struck Merryl behind the knees. He went down, Tiaan flying from his arms.

It made all the difference. In a few strides Vithis was on them. Lifting Tiaan effortlessly in one arm, he drew his sword with the other hand. She struggled but he crushed her against his side, his arm squeezing the air from her lungs.

'Keep your distance!' he roared at the human soldiers. 'Tiaan stole what was mine and I will have it back.' More Aachim ran up to support him.

The soldiers skidded to a stop, swords drawn. Their line parted and a handful of black-robed figures pushed between them, including a tall, burly man and a short one with only one arm. His face was covered by a platinum mask.

'My name is Ghorr,' said the big man, 'Chief Scrutator. Give up the artisan, Lord Vithis.'

'I'll go to war against all humanity first; hissed Vithis.

More Aachim were running up all the time. Already they outnumbered the humans. Behind them Tiaan was pleased to see that the construct was blazing head high. With a loud bang, pieces of metal spun through the air. The secret of flight — the diamond hedrons and carbon whiskers — would be burned to vapour. Only Malien knew, and Tiaan herself. But could she keep that secret from Vithis?

Ghorr raised a clenched fist, took one step forward, then stopped.

Tiaan trembled in Vithis's arms, but the scrutators could not find the courage to attack him. With a sneer of contempt, Vithis turned his back and headed for the Aachim camp.