“Yes,” said Isaac. “That’s how this is going to work. I forgot some of the components of the crisis engine when I left it with you, which is why it wasn’t complete. But that’s just as well, because when I saw them, they gave me the idea for all this. But listen: I need your help. If this is going to work we need the maths to be exact. I brought my analytical engine with me from the laboratory, but it’s hardly a top-notch model. You, Council, are a network of damn sophisticated calculating engines . . . right? I need you to do some sums for me. Work out some functions, print up some programme cards. And I need them perfect. To an infinitesimal degree of error. All right?”

“Show me,” said the avatar.

Isaac pulled out two sheets of paper. He walked over to the avatar, holding them out. In the dump’s smell of oil and chymical mould and warming metal, the organic stink of the avatar’s slowly collapsing body was shocking. Isaac creased his nose in disgust. But he steeled himself and stood beside the rotting, half-alive carcass and explained the functions he had outlined.

“This page here is several equations I can’t get the answers to. Can you read them? They’re to do with the mathematical modelling of mental activity. This second page is more tricky. This is the set of programme cards I need. I’ve tried to lay out each function as exactly as I can. So here for example . . .” Isaac’s stubby finger moved along a line of complicated logic symbols. “This is ‘find data from input one; now model data.’ Then here we have the same demand for input two . . . and this really complex one here: ‘compare prime data.’ Then over here are the constructive, remodelling functions.

“Is that all comprehensible?” he said, stepping back. “And can you do it?”

The avatar took the papers and scanned them carefully. The dead man’s eyes moved in a smooth left-right-left motion along the page. It was seamless until the avatar paused and shuddered as data welled along the cable to the Construct’s hidden brain.

There was a motionless moment, and then the avatar said: “This can all be done.”

Isaac nodded in curt triumph. “We need it . . . well . . . now. As soon as possible. I can wait. Can you do that?”

“I will try. And then as evening falls and the slake-moths return, you will turn on the power, and you will connect me. You will link me up to your crisis engine.”

Isaac nodded.

He fumbled in his pocket and drew out another piece of paper, which he handed to the avatar.