“Don’t worry, Yag. You’ll get what you’re after. As far as you’re concerned, what this means—if I can make it work—is that I can turn you into a walking, flying dynamo. The more you fly, the more crisis energy you manifest, the more you can fly. Tired wings are a problem you won’t face no more.”

There was a troubled silence at that. To Isaac’s relief, Yagharek did not seem to have noticed the unfortunate double-meaning. The garuda was stroking the paper with wonder and hunger. Yagharek murmured something in his own tongue, a soft, guttural croon.

Eventually he looked up.

“When will you build this thing, Grimnebulin?” he asked.

“Well, I need to actually knock together a working model to test it, refine the maths and whatnot. I reckon it’ll take me a week or so to put something together. But that’s early days, remember. Very early days.” Yagharek nodded quickly, waved away the caution. “You sure you don’t want to kip here? Are you still going to wander round like a ghul and spring on me when I least suspect it?” asked Isaac ironically.

Yagharek nodded.

“Please tell me as soon as your theories advance, Grimnebulin,” he asked. Isaac laughed at the polite bathos of the request.

“Certainly will, old son, you have my word. As soon as the old theories advance, you get to know.”

Yagharek turned stiffly and walked towards the stairs. As he turned to say goodbye, he caught sight of something. He was still for a minute, then walked over to the far end of the walkway’s east-facing side. He indicated the cage containing the colossal grub.

“Grimnebulin,” he said. “What does your caterpillar do?”

“I know, I know, it’s grown like fuck, hasn’t it?” said Isaac, strolling over. “Tremendous little bugger, eh?”

Yagharek pointed at the cage and looked up questioningly.

“Yes,” he said. “But what does it do?”

Isaac frowned and peered into the wooden box. He had moved it so that it faced away from the windows, which meant that its interior was shadowed and unclear. He squinted and peered into the darkness.

The massive creature had crawled to the furthest corner of the cage and had somehow managed to climb the rough wood. Then, with some organic adhesive it exuded from its arse, it had suspended itself from the top of the box. It hung there, pendulous and heavy, swaying and rippling slightly, like a stocking full of mud.

Isaac hissed, his tongue jutting from between his lips.

The caterpillar had tightened its stubby legs, curling them in tight towards its underbelly. As Isaac and Yagharek watched, it jack-knifed at its centre and seemed to kiss its own tail end, slowly relaxing until it hung deadweight again. It repeated the process.

Isaac pointed into the dimness.

“Look,” he said. “It’s smearing something all over itself.”