Hampstead’s wealth lay unconscious along the edge of the Heath, Mercedes and SUVs frosted beneath plane trees, Victorian terraces unlit. A Starbucks glowed, but otherwise the streets were dark. The first solitary commuter cars whispered down Willow Road to South End Green. Detective Constable Nick Belsey listened, counting. He heard three in a minute, which meant it was before six am. Ice outlined the leaves and branches around him and the earth was cold beneath his body. His mouth had soil in it, and there was a smell of blood and rotten bark.

Belsey lay on a small mound on the southern side of Hampstead Heath. The mound was crowded with pine trees, surrounded by gorse and partitioned from the rest of the world by a low, iron fence. So it wasn’t such an absurd place to seek shelter, Belsey thought, if that had been his intention. His coat lay on the ground. A throbbing pain travelled his body, too general to locate one source. His face was involved; his upper body. The detective stood up slowly. He shook his coat, put it on and climbed over the fence into long grass.

From the hilltop he could see London, stretched towards the hills of Kent and Surrey. The city itself looked numb as a rough sleeper; Camden and then the West End, the City, tower blocks puncturing a thin mist. He admired the fragile light. His watch was missing. He searched his pockets, found a blood-stained serviette and a promotional leaflet for a spiritual retreat, but no keys or phone or police badge.

He walked to the athletics track and along the path to the ponds. His shoes were flooded and water seeped between his toes. He crossed the bridge that divided the mixed bathing pond in two and looked for early swimmers. None yet. He knelt on the concrete of the bridge, bent to the water and splashed his face. Blood dripped from his shaking hands. He leaned over to see his reflection but could make out only an oily confusion of light and darkness. Two swans watched him from beside the diving platform. ‘Good morning,’ Belsey said. He waited for them to turn and glide a distance away then plunged his head beneath the surface.