She turned back to the crowd, sharp for clues. Most faces were monotonous: displaying happiness or boredom, stress or fatigue. Somewhere nearby a child screamed and burst into tears. In the opposite direction, somebody leaned on a car horn, its blast momentarily turning heads.

She was about to concede defeat when a couple emerged directly ahead, the middle-aged woman rubbing her shoulder, twisting to glare back along the street.

Good enough.

Hawkins took off in that direction.

Ahead, two teenagers vacated a bench and Hawkins took her chance, leaping on to the stone surface, staring out over the hordes. At first, she saw nothing but bobbing heads filling the pavement, a maelstrom of hats and umbrellas. She stifled a growl, about to dismount.

When she saw him.

The watcher stepped out of the crowd no more than twenty yards ahead, and began walking casually along the bus lane at the side of the road. He turned to check he wasn’t being followed, but his gaze was concentrated on the mass of people directly behind him. He didn’t seem to notice Hawkins staring at him over a thousand other heads.

But she had already gone.

Hawkins stepped into the road behind a red double decker that belched heat as it passed, rainwater hissing from its tyres. Behind it, a gap allowed her to see the watcher facing forwards once more, now moving at a brisk stroll, skipping on and off the pavement to avoid two passing black cabs.

Clearly the watcher thought he was out of immediate danger, his glances to check he wasn’t being pursued dropping in frequency the further they went.

Hawkins took full advantage of his complacency, closing the gap to ten yards, sliding back into the crowd whenever his shoulders started to turn. Her pocket began to vibrate and she pulled her mobile free, checking the screen, realizing she hadn’t reinstated the volume after their meeting with Joseph White.

She answered. ‘Chris, where are you?’

‘Outside John Lewis … ma’am.’ Chris was breathing heavily. ‘I didn’t see which way you … went.’

‘It’s OK,’ she said, dodging back on to the kerb. ‘I’m still with him, heading west along Oxford Street. Follow us down, stay on the line.’

She kept the phone to her ear, forced to sidestep a couple of youngsters in beanie hats and wait for another bus to roar past before she could return to the road.

At exactly the wrong moment.

She locked eyes with the watcher, whose latest check had coincided with her emergence from the crowd. They stayed like that for a split second, and Hawkins had just opened her mouth to declare her credentials when he turned and took off.

She broke into a sprint, telling Chris to hurry up, unable to hear his response as a car horn blared at her target, its headlights flashing in the gathering gloom.