He almost whistled. ‘A QPM? Was it for exceptional courage, skill, exhibiting conspicuous devotion to duty, or all three?’ He laughed. ‘Lucky he had a bomb in his bag. Or they would have given you twenty years to life.’

‘It’s good to have you, Wolfe,’ Whitestone told me, ending the chat. ‘The boss is waiting for you.’

SOCOs were putting up arc lights at the end of the alley where Mallory stood next to a black shape lying on the ground by giant recycling bins, his long lean figure stock still in the blazing white glare as the scene was carefully prepared, looking like an actor waiting for his cue to step on stage. The filthy alley felt like it was light years away from the shining tower where we had found Hugo Buck.

‘I thought we had another one,’ I said.

‘We do,’ Mallory said.

There’s a look that you see in all boxers and in certain breeds of dog – German Shepherds have it. It is a look that reveals knowledge of how serious the world is. Mallory had that look now.

‘Different postcode, same killer,’ he said. ‘Look.’

The dead man wore the sad rags of homelessness. And someone had cut his throat out.

All of it.

The fierce white lights revealed a neck that had been ripped open, torn out, the front half of the victim’s neck cleaved clean away. Again. It felt like only the spine was keeping the head attached to the body. Again. Mallory was right. The homeless man in the stinking alley was a world away from the banker in his glass tower.

But he was another one.

Even under the arc lights the alley was cold, and through the thin rubber gloves I could feel the sweat tingle on my palms.

I turned on my torch to look beyond the reach of the lights’ glare, and let the thin beam trace slowly across the great spurts of arterial blood covering the walls and the recycling bins. I turned the torch off as I looked at the blood that soaked and stained the top half of the body.

The blood stank with that distinctive metallic odour that is also sickeningly human, and the smell mixed with the fuel and food and alcohol scents of the West End.

I tried to look beyond the blood and the horror. I tried to look at what had once been a man.

His hair was long and matted, the clothes rags, blackened by the grinding toll of living on the streets. It was hard to estimate his age because he looked all used up, as though he had lived an entire lifetime long before this brutal death.

‘There will be needle marks on his arms,’ I said, ‘and perhaps on the legs, and even between the toes.’

Mallory said, ‘But why kill a man who was so busy killing himself?’