‘Not them. It’s the rats, Max. The millions of rats down there. The sniffer dogs don’t have a chance picking up a trail in a world full of rats.’

‘I want you to talk to Professor Hitchens later today,’ the Chief Super said. ‘There might be something you recall about the kill site that will ring some bells for him.’

‘Yes, ma’am.’

‘There’s one thing I don’t understand . . .’ Whitestone said.

I waited.

‘Why aren’t you dead, Max?’ she asked.

I had told Edie Wren everything that I could remember but I had not mentioned the Glock 17. Because I did not know where to begin with the Glock and I did not want my friend to go to jail.

But I knew that our people must have found the gun by now.

‘The pipe they hanged me from broke and they took off,’ I said in reply to Whitestone’s question. ‘Just lucky, I guess.’

Whitestone and Swire exchanged a look. I knew what was coming so I got there first.

‘And they couldn’t shoot straight,’ I said. ‘I managed to get hold of their firearm after it was discharged. Presumably you’ve found it by now? Some kind of Glock. I’m no firearms expert.’

Whitestone glanced at her notes.

‘Yes, a Glock,’ she said. ‘The search team found it down on the tracks of that old tube station.’ She looked at me levelly, reading me the way I had seen her read so many faces in interview rooms. ‘A Glock Safe Action Pistol,’ she said. ‘The British Army like them. Standard issue, apparently.’

‘Forensics will find my prints all over it,’ I said.

‘You shot at them?’ Swire said, her face darkening.

Every time a member of the Metropolitan Police discharges a firearm, he or she triggers an enquiry that treats him or her as a potential criminal. You are arrested. You are investigated. Unemployment and incarceration are both real possibilities just for pulling that trigger. Even if you shoot Osama bin Laden. And that’s what they do to our highly trained Specialist Firearms officers, the Armed Response Vehicle officers and Tactical Support officers – the specialist police who are actually meant to be carrying a gun.

I had no idea what they would do to someone like me and I wasn’t anxious to find out.

‘The magazine was empty by the time I had the weapon in my hands,’ I said. ‘I pulled the trigger but it didn’t go bang. I took it with me for evidence and dropped it when I got out of the way of a train.’

Silence.

They looked at each other and back at me. They were not sure if they wanted to buy it. I found I did not care.

‘What about PC Rocastle?’ I said.

‘Who?’ said the Chief Super.