“That old bastard hit me!”

“He said it was the only way to get rid of the one-armed man you keep conjuring up. Well, he said killing you would work too.”

“You don’t even recognize him, do you?”

“Who?”

“The one-armed man!”

“Should I?”

“Well, you’re the reason he’s one-armed!”

With a grunt Snorri heaved himself over the top of the ladder and shrugged me off onto the floor of a small chamber. I lay groaning as Kara and Hennan joined us. Screens and access panels dotted the walls, the remaining space being thick with pipework. Three narrow tunnels ran off, one vertically.

“Where are we?” What I really meant was where was Cutter John?

“Inside the machine,” Kara said. “The professor gave me a map to the place where we can use the key.” She peered down the shaft we’d just come up. “He said that the shielding is stronger in here, so your friend might take a bit longer to find us.”

“Except where it’s not,” Hennan added.

“Sorry?” I had a quick glance over the edge myself. Nothing.

“The shielding is stronger in most places. But there are unshielded areas too,” Kara said. “They’re marked with yellow warning signs.”

I clambered to my feet, using the wall for support, and pulled my hands free of their bindings. “Let’s get on with it then.” I gestured for Kara to lead on. She consulted the paper in her hand and led off down the passage to the left.

I walked at the rear, rubbing the back of my head. If having a walking stick broken over my skull hadn’t given me a headache then the pulsing of the dim lighting and the pervasive throb of the hidden machinery would have. The cramped conditions were claustrophobic on their own but it managed to be much worse than that. The still air held a sickly-sweet stink and the walls pressed close, as if at any moment the Builders’ engine might flex its muscles, snapping shut the already-tight voids within it.

Up ahead the passage opened into a chamber just big enough for the four of us to stand together, then led on. As I squeezed in Kara had just set her fingers to an irregular-shaped mirror panel set into the wall. The reflection it offered seemed fuzzy at the edges and several smaller reflections of Kara jumped into being where her fingers made contact. Without warning her face vanished from the mirror to be replaced by the professor’s.

“Ah, I see young Jalan has recovered! Let him be the one to use the key. An imagination as overactive as his has . . . drawbacks . . . as we’ve seen, but it should allow a strong bond with the key and enhance the effects of—”

“What is this thing?” I interrupted.

“What thing?”

“This!” I leaned past Kara and jabbed at the professor’s image. “It was a mirror.”

“Well.” The professor puffed himself up like a tutor about to dispense wisdom. “It would take very long time to list all its functions, but it serves a variety of important uses in the main analysis suite, perhaps communication being the most minor. You’ll see numerous such panels as you follow the route to the central processor, but they’re all actually the same object. It’s very difficult to explain . . . we call it a fractal mirror—”

“Break it, Snorri! Quick!”

Convinced by my tone, for once Snorri did as he was told, and with a violent thrust drove the horns of his axe into the professor’s face.

“You can’t break it!” The professor favoured us with an indulgent smile as the axe slid over his image, leaving no mark. “Why would you even want to?”

“The Lady Blue is going to use the mirror to come here . . . if she’s not here already. She can watch through mirrors and if she sees us, well, we’re in trouble: she doesn’t want the Wheel stopped.”

“If you break the mirror the magnetic confinement will become unstable. All manner of processes may drift beyond their designated bounds . . .”

“We’re here to turn the engine off. It doesn’t matter if we damage it a bit beforehand.” The Lady Blue could glance our way at any moment. The mirror was her last escape route from her tower in Blujen: she would hardly ignore it. The panic that had been bubbling away in me, up to about chest height, ever since I regained my senses now started to rise toward my eyes.

“Well . . .” Professor O’Kee pursed his lips. “You would have to go down to the original mirror in Hall E. It’s marked on the map. But if you break the prime image you might only have minutes left.”