“Do you understand?” Rove demanded. “It shows best guesses, probabilities based on the tracking machines here. Pathetic, really. Machines as big as a house trying to penetrate the interdimensional membranes, and this is the best they can give us. Find them, Lucas. We need the doctor unharmed. Use Pryor as leverage against her allies. They seem to be very keen on keeping her alive.”

“Understood,” Lucas said. He stared at the bewildering scatter of data. Sheep, and we’re the dogs. Their focus was southeast from their location, a chaotic swirl of probability covering two or three streets.

He barked out orders to the other three. He and Amin would follow behind, Terrence east, Josef west. It would be like old times, when all that expensive technology could take you only so far and no further. It would be down to using their eyes, dragging those faces out of a crowd and looking for body language that said “fugitive,” for people trying not to be seen.

Hanging back was the worst part: necessary because he’d screw with the App, because Pryor knew his face. And he was looking forward to seeing her face again; three good people were dead because she hadn’t sat still. Just because Rove wanted her as a bargaining chip didn’t mean he couldn’t slap some sense into her. Or he could stamp on a knee, teach her a valuable lesson about what a privilege running away can be. Lucas wasn’t an angry man by nature, but he had a keen sense of when he’d been wronged, requiring due compensation from the guilty parties.

On his phone, the dots were coalescing into something more concrete: from a scatter of streets to a couple. Lucas watched and gave his people instructions as they closed in.

Abruptly the display on the screen jumped, everything imploding so that for a moment he thought they’d lost the trail entirely. But no: there was a dot left over: a single possibility, which meant it was a certainty.

He had someone right there, but his heart sank when he saw who it was. “Terrence, what’s your position?”

“Heathcote Street, sir, waiting for your word.” Sounding super-extra earnest and vigilant.

“You don’t see them anywhere near you?” On Lucas’s phone the dot was beginning to expand again, to fuzz from indisputable fact into vague rumour.

“No-o.” But there was a slight hesitancy in Terrence’s voice.

Lucas signalled Josef to close the trap on Terrence’s location and diverted Amin to come round from the other side.

“What?” he demanded, making double-quick time himself.

“Nothing,” Terrence said defensively. “Saw a girl who might have been Pryor, but she was with another woman, not the doc.”

Lucas’s mind went blank for precisely three-quarters of a second, before flaring into life. “You fuckwit, you didn’t read the brief, did you? Go after them!”