After that there was quite a long pause. Kearney heard two or three small movements, as of someone removing a book from a shelf; then an intake of breath. “Listen to this—” Sprake began, but fell silent immediately. When Kearney came out of the kitchen, the street door was open and the apartment was empty. Two or three books lay on the floor, surrounded by torn-out pages which looked like wings. Onto the empty white wall above the sofa, in a bright parallelogram of sodium light, something outside was projecting the shadow of an enormous beaked head. It looked nothing like the head of a bird. “Christ,” said Kearney, his heart beating so hard he could feel it rocking his upper body. “Christ!” The shadow began to turn, as if its owner, hanging in the air two storeys above a street in Chiswick, two in the morning, was turning to look at him. Or worse, as if it wasn’t a shadow at all.

“Jesus Christ, Sprake, it’s here!” Kearney shouted, and ran out of the apartment. He could hear Sprake’s footsteps thudding on the pavement somewhere ahead of him; but he never caught him up.

Central London, 3 a.m.

Fractals spilled across icy blue displays, developing into something that resembled the jerky frame-by-frame slow motion of a much earlier medium. Brian Tate rubbed his eyes and stared. Behind him, the suite was dark. It smelled of junk food, cold coffee. The male cat was sniffing about in a litter of discarded polystyrene cups and burger cartons around Tate’s feet. The female sat quietly on his shoulder, watching with a kind of companionable complicity the mathematical monster unspooling across the screens in front of them. Every so often she dabbed out a paw, mewing impatiently, as if to draw Tate’s attention to something he had missed. She knew where the action was. Tate took off his glasses and put them on the desk in front of him. Even at these speeds there was nothing to see.

Or almost nothing. At Los Alamos, bored—though he would never have admitted it to anyone—by the constant talk about physics and money, he had spent most of his free time in his room, switching restlessly from TV channel to TV channel with the sound turned down. This led him to think about choice. The moment of choice, he thought, could be located very exactly as one image flickered, broke and was replaced by the next. If you levered things apart, if you could get into the exact moment of transition, what would you find? Entertaining himself with the fantasy of an unknown station—something more watchable than reruns of Buffy the Vampire Slayer—transmitting into the gap, into the moment of choice, he had tried to record a series of channel changes on the VCR and play them back in stop-frame. This had proved to be impossible.

He reached back to stroke the cat’s ears. She evaded him, jumped down onto the floor, where she hissed at the male until he retreated under Tate’s chair.