Hawkins drifted forwards, glimpsing Chris on the adjacent pathway, peering behind a low hedge as she went back to her own search. The park was crowded and noisy, the rain having eased, prompting more pedestrians to gather in front of the bandstand. Plenty of others kept moving, trying to get out of the city before nightfall. People crunched along the gravel pathways criss-crossing the public area, some with straggling kids; others walking alone, heads down and hoods up against the cold. Her gaze flicked from person to person as she moved, no longer just picking up detail; now alert for behaviour as well – motion that might signify someone trying too hard to blend in.

At first there was nothing but a sea of winter coats sliding past one another.

Then it came.

Hawkins’ gaze lingered on a lone girl twenty yards away, hands stuffed in the pockets of a fluffy-collared coat as she swung off the path on to the grass, to let two mothers with prams pass unimpeded. The manoeuvre took her close to a large tree.

Hawkins almost looked away, but something held her interest.

The girl had looked up – not in the direction she was going, but sideways, as if something had drawn her attention.

Something she hadn’t expected to see.

‘Chris!’ Hawkins shouted, advancing. And as she moved, someone leaned out from behind the tree, remaining in sight just long enough to confirm that their cover was blown. But also long enough for Hawkins to recognize the watcher.

‘He’s here!’ she barked, hearing the scrape of gravel as Chris took off behind her, both of them sprinting after the grey parka jacket now running full pelt towards the park’s southern boundary.

‘Met Police!’ Hawkins shouted, twisting past the baffled faces blocking her path, thanking good fortune that she’d chosen thick-soled biker boots that morning, rather than their spike-heeled equivalents.

But the watcher held a twenty-yard lead as Hawkins flashed past his abandoned hiding place, and they were nearly halfway to the thick line of foliage that formed the garden’s perimeter. Hawkins tried to predict his next move.

The park’s walkways were laid out in a large cross, with exits at all four corners, so if he wanted to use one of those, he’d turn sharply any second now. Except, as he trampled the low greenery surrounding the sculpture and kept going, Hawkins realized he wasn’t going to change course. Instead he disappeared among the tall plants at the gardens’ edge.

Hawkins took a short detour, managing to leap a thinner section of the hedgerow, gaining a stride or two, skidding across the path and into the vegetation after their quarry, following the sounds of thrashing up ahead.

She shouldered her way between thick, head-height foliage which grabbed at her long wool coat, emerging just in time to see the watcher’s legs disappear over the sturdy metal barrier on top of a six-foot wall.