She began to sense a structure to the mist. It was like a series of scalloped platforms connected by stairs and ladders, though that could hardly be a part of the air-dreadnought. It was a creation of the Art, but Irisis couldn’t tell whether it was Yggur’s strange Art or Ghorr’s scrutator magic.

As they reached the level of the four main airbags, the air-bags appeared transparently in the distance, as if this place were only partly of the real world. Rigging ran between them, holding them in place, though here it appeared like strands drawn out of cloud or webs spangled with dewdrops. Tenuous paths led down and up, into nebulous cloud chambers. Between them, staircases ran to airy pavilions, arches and gates that had no part in an air-dreadnought’s rigging.

The flashes, now blue and red, came from higher up. Irisis put one foot out towards the first of the staircases.

Ullii snatched at her arm. ‘Not there!’

Irisis stepped back onto firmness then probed ahead with her sword. It went straight through what had appeared to be solid matter. The staircase was a deceit. Were any of the stairs and pavilions real, or was it a snare as cunningly designed as a spider’s web?

‘How did you know?’ she said, shaken.

Ullii let go of her arm. ‘I can still see,’ she said with that all too familiar hint of scorn that made Irisis smile. Ullii wasn’t as deep in despair as she made out.

‘Perhaps you’d better lead the way.’

Ullii went up, across and up again, stepping sure-footedly, always seeing the true paths among the traps and deceits Yggur and Ghorr had set for each other, which Irisis could not detect even with her fingers wrapped tightly around her pliance and the field streaming through her inner eye.

Up here she encountered deck upon deck, terrace upon terrace, pavilion upon pavilion, all linked like a misty maze, but one step off the unseeable path and they would fall fifty spans into the swamp forest.

‘Dwarf!’ said Ullii as they rounded a mist bank surrounded by a shimmering rainbow in shades of green and yellow.

A span or two off the path, trapped in a cell shaped somewhat like a pumpkin, the little man clutched at the bars. Klarm looked at Irisis, she at him.

‘Should I set you free or leave you here where you’re safe?’ said Irisis.

‘If you don’t free me the right way, the cell will simply dissolve into bottomless air,’ said Klarm.

‘And if I leave you here?’

‘If Ghorr is defeated, or victorious and so chooses, the cell will simply dissolve into bottomless air.’

‘Then I’m not taking much of a risk. But just in case, tie on to this.’ She passed one end of her line through the bars, tied the other around her hips, took Klarm’s hand and braced herself.

‘Ullii?’ said Irisis, acting on a hunch.

Ullii cursed Irisis under her breath, but put her hand to the lock and the cage melted into empty air, giving the lie to her earlier words about losing her lattice. Irisis, with some effort, swung Klarm up onto a solid footing.

‘Where’s Yggur?’ she said.

‘He was up there, earlier,’ said Klarm, pointing between the topmost airbag and the starboard one, where a gauzy path branched into three. The middle path passed through a triumphal arch, though nothing could be seen beyond it but blue-black emptiness. The right path terminated at what appeared to be a stone garden seat, while the left one wound off into mist. ‘But this labyrinth changes all the time. I don’t know where he is now. Ghorr may have him already.’

‘How did it get here?’ Irisis said as they mounted a stair like airy crystal.

‘Ghorr hunted Yggur up here and Yggur created this place as he went – it was the only defence he had the strength for. Even here, at the seat of Yggur’s power, it was the one shelter he could make without the aid of crystals or artefacts.’

‘But it didn’t work.’

‘It saved his life but he can’t escape it. Ghorr is the father of scrutator magic and he’s got a whole air-dreadnought full of crystals and devices to store and channel his power. Every deception Yggur creates, Ghorr sees through it. And now Ghorr is starting to take control of the labyrinth, and turn its traps and deceptions back on its maker.’ A dull red flash carved slices off the sky above them. ‘See how weak he is. In a few minutes it’ll be over.’

Ullii led them to another cell, this one a cube of glassy nothingness not unlike the steps they were standing on. A bloodstained Flangers, with minor wounds in a dozen places, had been imprisoned inside it, spread-eagled. Ullii freed him as she had Klarm and he hobbled after them.

They mounted a bifurcating ramp to a higher level, a sheer white plane on which rolled two enormous spheres. The nearer one was three or four spans across and made of smoky glass with a metallic lustre. A smaller sphere moved inside the larger, though Irisis could not see what it contained. The distant sphere was even bigger, completely transparent, and contained innumerable smaller spheres, all rolling about inside the larger one.

‘That’s Yggur,’ said Ullii.

A feeble red flash lit up one of the small spheres and they saw a tiny figure inside, staggering from one rolling, tumbling sphere to another like a rat trapped in a maze. The red light silhouetted the occupant of the nearer sphere and it was unmistakably Ghorr.

White light jagged out from Ghorr’s hand, illuminating Yggur’s outer sphere and licking around the outside until it found a way in. One of the inner spheres glowed green, went dark and disappeared. Shortly Irisis heard a faint tinkle, like glass smashing. Looking more closely, she saw that a number of the small spheres had already imploded, leaving just transparencies as tenuous as soap bubbles.

‘If Ghorr catches Yggur inside one …’ said Irisis.

‘With a thousand shards of glass driven through his body, it’ll be the end of him,’ said Klarm.

‘He’s doomed anyway, surely?’

‘As long as there were lots of spheres he could outguess Ghorr. Once there are only a few, sooner or later Ghorr will pick his destination at the same time as Yggur jumps.’

‘It’s not Yggur’s way to be trapped like that. He’ll come out first and attack head-on.’

‘He’s too weak. Ghorr would annihilate him.’

‘Then we’ve got to stop Ghorr.’

‘What if I were to attack his sphere from behind?’ said Flangers. ‘I could take Irisis’s sword.’

‘The sphere was created with the Art,’ said Klarm. ‘You couldn’t break it with a sword, and as soon as you tried he’d roll right over you.’

‘It might give Yggur the chance he needs,’ said Flangers.

‘And you might be throwing away your life for nothing,’ said Irisis. ‘No, Flangers – sword against sword but the Art against the Art. What can we do, Klarm?’

‘Ghorr still holds the keys to the chief scrutator’s chest and, despite his earlier setbacks, he’s still the strongest of all the Council. If he can overpower Yggur, or take him alive, the other scrutators will support him. They worship power – it’s the very meaning of the Council’s existence. Although Ghorr stands revealed as a coward and a vicious thug, if he has the power he holds the Council in his hand.’

Ghorr’s sphere rolled the other way, emitting a double flash that burst two of the glassy bubbles inside Yggur’s sphere. It spun crazily and wheeled off, wobbling across the floor, the figure inside staggering like a drunk.

His options were shrinking to nothing, and Irisis couldn’t let that happen. ‘Ghorr has to be overcome. He must fall.’

‘He stripped me of my scrutator magic before he put me in that cell,’ said Klarm. ‘I can’t stop him and I don’t think anyone can.’

They were above the mist here. Irisis looked back at the survivors of the air-dreadnought fleet, which had gathered over Fiz Gorgo and were turning towards them. ‘What about Fusshte?’ His craft was heading in their direction and she could see him at the bow.