The grub waved its thick head blindly. It shifted its massive body sluggishly around the wire prison. It was at least four inches long and one inch thick, with bright colours slapped randomly around its chubby cylindrical body. Spiky hairs sprouted from its rump. It shared its cage with browning lettuce leaves, little snips of meat, slices of fruit, paper strips.

“See,” said Isaac, “I’ve tried to feed the thing everything. I’ve put in as many herbs and plants as exist, and it doesn’t want any of them. So I tried it on fish and fruit and cake, bread, meat, paper, glue, cotton, silk . . . it just roots aimlessly around being hungry, staring at me accusingly.”

Isaac leaned in, planting his face between David’s and Lublamai’s.

“It obviously wants to eat,” he said. “Its colour’s fading, which is worrying, both aesthetically and physiologically . . . I’m at a loss. I think the beautiful thing’s going to sit there and die on me.” Isaac sniffed matter-of-factly.

“Where did you get it from?” asked David.

“Oh, you know how this stuff works,” said Isaac. “I got it from a cove who got it from a man who got it from a woman who got it . . . and so on. I’ve no idea where it came from.”

“You’re not going to cut this open, are you?”

“ ’Stail, no. If it lives to build a cocoon, which I’m afraid I doubt, I’ll be very interested to see what comes out. I might even donate it to the Science Museum. You know me. Public-spirited . . . So anyway, this thing’s not really much use to me for research. Can’t even make it eat, let alone metamorphose, let alone fly. So everything else you see around you—” he spread his arms wide, wriggled his wrists to take in the room “—is grist to my counter-gravitational mill. But this little geezer—” he pointed at the listless caterpillar “—this is social work.” He grinned widely.

There was a creaking from below. The door was being pushed open. All three men lurched dangerously over the side of the walkway and peered down, expecting to see Yagharek the garuda, with his false wings under his cloak.

Lin peered up at them.

David and Lublamai started in confusion. They were embarrassed at Isaac’s sudden cry of irritated welcome. They found something else to look at.

Isaac was scurrying down the stairs.

“Lin,” he bellowed. “Good to see you.” When he reached her he spoke quietly.

“Sweetheart, what are you doing here? I thought I was going to see you later in the week.”