‘A Glock 17. Belonged to an ex-serviceman friend of mine. I’ll not tell you his name, if that’s OK.’

‘I don’t need to know his name, Max. But you were armed?’

‘I took it from my friend because I was afraid of what he might do with it. And I took it with me to Abu Din’s house because I thought the Hanging Club would not hesitate to kill me to get to Abu Din. I was going to get rid of it after that, chuck it in the Thames from the middle of a bridge.’ I thought of young Steve Goddard Junior and his knife. ‘Or drop it down a drain,’ I said.

I was covered in a cold sweat at the memory of having the gun in my hand and wanting to kill them with it. It felt like I had broken enough firearms regulations to get slung out on my ear, or slung in a room with bars on the window. I silently thanked the heavens that it was our people who had found the gun.

‘Have you still got the Glock?’ John asked.

‘No.’

‘Good boy.’

He wasn’t interested in the gun any more. There are a lot of firearms in the Black Museum. Guns held no special fear or fascination for Sergeant John Caine.

‘Then you went after them,’ he said.

‘This is where it gets blurry. We were underground. And they went deeper underground. It was totally black – stairs that led to a tunnel that led to a passageway – big arched columns that were meant to process large numbers of people. It looked like a football stadium at first – it had that kind of epic quality to it, as though thousands of people were going to pass this spot.’

‘And it turned out to be an abandoned tube station.’

‘British Museum. You ever heard of it?’

He shook his head. ‘But London is full of disused underground stations. They’ve been closing them down since 1900. They were very busy during the Blitz. Since then, not so much. And they found you outside British Museum, right? It’s pretty central, Max.’

‘I know,’ I said, and we sipped our tea in silence. I could feel the sugar kicking in.

‘One other thing,’ I said. ‘When they were taking me to the kill site, they took me down a corridor, and it was like something from a nightmare, something from a fairy story. Because it kept getting smaller. It was Alice in Wonderland stuff. The roof came down, the walls came in, and by the time we got to the end of it I had my arms pressed against my side and my head hunched down.’

His face was suddenly white with shock.