WE DROVE BACK to the city. DCI Whitestone at the wheel of my X5. DI Gane beside her in the passenger seat. Edie Wren and me in the back. Every time I was drifting off, thinking I might steal some sleep, the road rushing under our wheels and the white-hot pain in my cracked ribs shoved me awake.

‘Sergeant Tom Monk came back from Afghanistan and he never went home,’ Whitestone said, her eyes not leaving the road ahead. ‘I spoke to the people at Barrington Court. Monk returned from Helmand with a Conspicuous Gallantry Cross and third-degree burns on his face and hands. He spent a few months in an ICU and then went to Barrington Court for his final rehab. Treatment for his burns. Extensive physio. Therapy sessions with a psychoanalyst. The usual routine for a veteran with his injuries. When he had recovered, he stayed on helping out at Barrington Court. And they were glad for an extra pair of hands. Nobody seems to know what happened. But just before he was due to leave Barrington Court, Monk put on his dress uniform and had his photo taken at a small studio in Potter’s Field High Street. Then he mailed the photo to his fiancée back in Stratford.’

Whitestone fell silent. I thought of the face that had been burned beyond recognition, and I thought of his girl back home, seeing a posed photograph of the damage for the first time.

The road kept slipping past, lit by nothing but the high winter moon.

‘Nobody knows if she ever wrote back. Or sent him a text, email or message on Facebook. Monk never talked about it. Maybe she told him that it was over. Maybe she never contacted him again and that told him all he needed to know. Who knows? But Monk never left Barrington Court. He stayed on – unpaid, unofficial, helping out with the rehab of other badly injured veterans. Taking the men to Potter’s Field for exercise.’

‘Where he met another old soldier,’ I said. ‘Len Zukov. The start of a beautiful friendship.’

‘I understand why Len Zukov wanted payback for what they did to his granddaughter,’ Wren said. ‘And I get why his friend would want to help him. But – did Monk want to kill evil bastards? Or did he just want to kill somebody?’

Whitestone glanced at me in the rear-view mirror. I had no answers. All I knew was that the state had trained Monk to be a killer and in the end that was all he had left, and all he could do, all he could offer, even when the state wanted him to stop.

‘Edie,’ Whitestone said. ‘Some stuff we never get to know.’

You could see the piercing blue lights of our cars cutting up the night from a mile away. They illuminated the sleek, futuristic buildings of the Olympic Park and the urban wasteland that surrounded them.