Where the caterpillar’s mouth touched flesh, it left infinitely thin glistening filaments, which stretched out taut as it moved its mouth away, adhering where they touched its body again. The hairs at the creature’s hind end were flattened against its body, and they looked wet. The enormous grub was slowly smothering itself in translucent silk, from the bottom up.

Isaac straightened up, slowly. He caught Yagharek’s eye.

“Well . . .” he said. “Better late than never. Finally, what I bought it for in the first place. The thing’s pupating.”

After a while, Yagharek nodded slowly.

“It will soon be able to fly,” he said quietly.

“Not necessarily, old son. Not everything with a chrysalis gets wings.”

“You do not know what it will be?”

“That, Yag, is the only reason I’ve still got the damn thing. Wretched curiosity. Won’t let me go.” Isaac smiled. The truth was he felt a certain nervousness, seeing the bizarre thing finally perform the action he had been waiting for since he had first seen it. He watched it cover itself in a strange, fastidious inversion of cleanliness. It was quick. The bright, mottled colours of its pelt went misty with the first layer of fibres, then quickly disappeared from view.

Yagharek’s interest in the creature was short-lived. He replaced the wooden framework which hid his deformity onto his shoulders, and covered it with his cloak.

“I will take my leave, Grimnebulin,” he said. Isaac looked up from where the caterpillar held his attention.

“Right! Righto, Yag. I’ll get a move on with the . . . uh . . . engine. I know by now not to ask when I’ll see you, right? You’ll drop in when the time’s right.” He shook his head.

Yagharek was already at the bottom of the stairs. He turned once, briefly, and saluted Isaac, and then he left.

Isaac waved back. He was lost in thought, his hand remaining in the air for several seconds after Yagharek had gone. Eventually, he closed it with a soft clap and turned back to the caterpillar’s cage.

Its coat of wet threads was drying fast. The tail end was already stiff and immobile. It constrained the grub’s undulations, forcing it to perform more and more claustrophobic acrobatics in its attempt to cover itself. Isaac pulled his chair over in front of the cage to watch its efforts. He took notes.

A part of him told him that he was being intellectually dissolute, that he should compose himself and focus on the matter in hand. But it was a small part, and it whispered to him without confidence. Almost dutifully. There was, after all, nothing that was going to stop Isaac from taking the opportunity to watch this extraordinary phenomenon. He settled into his chair comfortably, pulled over a magnifying lens.