The hairs stood up on the back of his neck. He scanned the mountain and immediately saw two figures, only minutes away. One was the Aachim witch-woman, the other Tiaan. As he ran down the ladder, something broke the air in the west. Three winged shapes, too big and bulky to be eagles or even skeets. They were lyrinx, and heading directly for the balloon.

He fled down the ladder, frantically undoing the ropes, though the balloon was not quite full enough to rise. Moreover, the basket had jammed between the rocks in its fall and would have to be worked free.

Nish hurled in his bag of pencil-stone, the packs and what remained of Ullii’s load. ‘Ullii!’ he yelled. ‘There’s no time. We’ve got to go.’

She made not a sound. He lugged her up, thrust his knife in his belt, decanted half a mug of tar spirits and scampered up the ladder. Lifting the lid off the brazier, he tossed the liquid in. It exploded in his face; Nish felt his hair frizzing. Slamming the lid, he leapt onto the nearest boulder and gave the basket a heave. It did not budge. It was jammed tight. Despair coiled around his heart. Not only was he going to lose the crystal but probably his life as well.

Jumping down between the boulders, he put his shoulder under the basket and heaved. It moved a fraction but jammed again. He tried the other side. The edge of the basket dug painfully into his shoulder. The basket scraped along the rock, then stopped.

The balloon was now as round as a globe and the ropes that held it to the basket were taut. It was ready to lift. Scrambling up the side, he shook the basket. It moved but did not free.

The lyrinx were descending rapidly now. The witch-woman was just fifty paces away. She threw out her arm, pointing at him.

Nish ducked. Golden sparkles burst in his eyes but he was otherwise unharmed. The witch-woman clutched at her chest as if in pain, then tottered forward. Nish shook the basket and felt something give. It lifted a handspan before jamming again.

If only he had a branch; anything to use as a lever. ‘Come on,’ he screamed, shaking it. ‘Just move!’

It did not. The witch-woman plodded around the boulders to come at him from the other side. She looked distressed. Nish wished a heart attack on the old fool.

‘Give up the crystal, artificer,’ she called.

‘Be damned!’ he snarled, ducking behind the basket for a rock.

She put out her hand, fingers hooked as if she were holding an egg, and slowly closed them. It was as though they had closed about his throat. Nish could not breathe. His face began to swell; his tongue was forced out through his lips. He gave a grunting squeal, which was answered by a moan from inside the basket.

Tiaan began to climb the rock. She had a length of metal in one hand. With a tremendous effort of will, he tore away from the Matah’s illusion and gasped a breath of air.

‘Ullii,’ he choked. ‘Save me.’

Ullii’s head appeared over the side of the basket, bobbing up and down. ‘Don’t know what to do,’ she quavered.

‘Throw something at the witch-woman. Try to knock her out.’ He groped for his knife.

Ullii hurled out her half-filled bag of pencil-stone, which flew wide, scattering black lumps everywhere.

‘Not the fuel!’ he screamed. ‘Haven’t you got a brain in your head?’

The seeker moaned. Then, to Nish’s horror, her chest pack, with its infinitely precious amplimet, soared out of the basket and struck the witch-woman in the face, knocking her down.

The pressure on his throat eased but before he could move Tiaan threw herself at him. He swiped at her but his knife was in the wrong hand and the blow missed. Tiaan thrust out the metal rod. He yelped, thinking she was going for his groin, but the rod went between his knees. She wrenched it sideways, his left knee collapsed and he toppled off the rock.

The fall seemed to take a long time. Nish thought he was going to land on his head, then his back. As he tumbled over, he realised that the knife was pointing up and he was likely to impale himself on it. He twisted in mid-air, slammed into the ground and felt a burning pain in his side.

He rolled over, groaning. Wetness flooded his shirt. A few steps away, the witch-woman was on her knees. Tiaan hurled herself on the pack. With a cry of triumph, she held up the amplimet.

Ullii wept. Nish groaned. His eyes met Tiaan’s, then slid sideways to where the wings of the descending lyrinx darkened the sky.

‘Enjoy your triumph!’ he gritted. ‘It won’t last long.’

‘Nor your tragedy,’ said Tiaan. ‘Goodbye, Nish. I hope we never meet again.’

‘We will,’ he said. ‘Oh yes, we will, artisan. Traitor!’

He hauled himself onto the rock. Tiaan was helping the witch-woman up the hill. Near the point where he had first seen them, they stopped, their backs to a jagged outcrop, and prepared to defend themselves.

Two lyrinx came gliding down in spirals. Was it better to flee, or hang around in case the battle gave him a chance to recover the crystal?

The first seconds dashed that hope. The witch-woman held out her arms and another of those shining bubbles, a huge one this time, burst forth to explode against the chest of the leading lyrinx. The creature seemed to freeze in mid-air, rolled and landed on its back. The second flapped away. He could not see the third.

Nish had seen enough. The witch-woman was too strong. The crystal was lost. He shook the basket and it moved up. Climbing in, he took hold of the balloon ropes and pulled down hard. It came a little way and rebounded. The ropes snapped taut and with a tearing of cane the basket slid out. They were away.

At last they were free of the heavy earth, where every step was a labour and the smallest river an impassable barrier. Up here, Nish felt in control of his life again. He did not have Tiaan, nor the crystal, but he had done the best he could. Most important of all, he had warned the scrutator about the invasion. Nish settled back. Just for a few minutes he was going to enjoy the ride.

The balloon shot up. Well above the level of the glacier, a strong wind pushed it away from the mountain, to the west. Nish frowned. He wanted to go east. Perhaps he should go down again, in some isolated place, and wait for a wind that would carry them the right way. That could be a long wait at this time of year. He reached for the release rope.

‘No!’ cried Ullii, holding her hands over her ears. ‘No, no!’

She was turning round and round, facing up at the sky. Her hands batted at the air; then, to his utter astonishment, she tore off the mask, exposing her naked eyes to the daylight. They were watering so much that pink tears ran down her cheeks.

‘Noooo!’ she screamed.

The third lyrinx had remained high up, on watch. Now it soared effortlessly after them. It was smaller than the others, no larger than a big man. Its outer, armoured skin was so transparent that he could see the more human inner skin beneath. It looked delicate, almost fragile, until Nish caught sight of the finger-long, extended claws.

Blood trickled down his side and Nish felt a momentary dizziness. Clutching one of the ropes, he stared at the approaching lyrinx. How would it attack? The basket was difficult to get at from the air; the creature would not want to risk tangling itself in the ropes.

Perhaps it would swoop down and come at them from below, or even try to knock him out with the Secret Art. All flying lyrinx were mancers – that was how they kept their massive bodies aloft. More lyrinx have died trying to fly on our heavy world than have been killed in the war, he recalled Scrutator Flydd saying. If he could distract it in some way he might have a chance.

Nish held out his sword, which made him feel better. He weighed the rope in his hand, balancing on the balls of his feet. The creature would have a harder job than it thought.