He left her bent over her notebooks. His exit elicited no more than a soft murmur and a slight inflection of her hand. He knew from past experience that she’d be like that, not moving except when absolutely necessary, blocking everything else out and using her ferocious concentration to map out all the little steps she’d made that preceded the giant leap drawn out in black marker.

Petrovitch left the university the same way he’d entered. Home for sure this time, beating the more spread out but nevertheless impressive migration to the outer parts of the Metrozone. He passed a copy of the iconic Underground map as he glided along the travelator, squashed to one side by a phalanx of marketeers who did nothing but talk into their headset microphones and eye up their prey.

He noticed that to get to Embankment, he’d have to go through St. James’s Gate. He shrugged his shoulders enough to be able to get into his bag, and look at the address on the evidence form he’d been left with.

The police station was just around the corner, and getting his hardware back was starting to become urgent. How long could it take to make a fuss at the front desk, threaten Chain with non-existent lawyers and finally get his hands on it?

He went through the screen, the turnstile, through the unconscious motions of traveling. There were three stops to go, then two, then one.

The lights flickered in a rippling pattern, from the front of the carriage to back, came on again. Then they snapped off, all the lights, plunging the passengers into utter, tunnel-enclosed darkness.

The train faltered, losing power to the motors, and someone banged hard into Petrovitch’s side, driving the air from his lungs and causing him to collide with half a dozen soft, yielding shapes who cushioned the impact.

He thought he was going to fall, to slide under their feet and become trampled. At the last moment, he found vertical again.

He was almost catapulted the other way when the lights blinked on and the train surged forward. He snaked out an arm and held tightly on to a pole, looking back down the chasm his wild movement had carved in the crowded carriage.

At the far end, even as the sea of people closed the gap, was a woman, a teenager with puff-ball white hair, a black jacket that was all zips and buckles, an object in her hand that was made from transparent plastic but had a single serrated edge.

He used his free hand to press against his T-shirt; no wetness, no spreading stain. But his courier bag had a hole in it, just about kidney height. They made the damnedest things out of kevlar these days.