He was shaking now, sweating, and it must have been obvious to him that the game was up. He’d been both unlucky and careless. He should have closed the door to his secret room when he went to get a fresh pack of cigarettes. But, of course, he hadn’t expected me to turn up and zap him with a Taser gun.

‘I’m not saying another word until I speak to a lawyer,’ he said.

The urge to kick him again was strong, but I resisted.

‘Suit yourself,’ I said.

I dashed back into the living room and called DCS Drummond. He answered on the second ring but before I could get a word in he told me that another police officer had been murdered. The news hit me hard, but I was more angry than shocked.

‘WPC Leah Campbell was shot while sitting in a patrol car along the South Bank,’ he said. ‘I’m at the scene now and it’s not pretty. Three bullets were fired into her body from close range, most likely by someone leaning through the side window.’

‘Christ almighty.’

‘She was parked up while waiting for her partner, who, believe it or not, was paying a visit to his girlfriend in a nearby block of flats. He discovered her body when he returned to the car.’

‘And you reckon she’s another victim of our assassin?’

‘I’d put money on it,’ he said. ‘The last text warned us that every cop in London was a potential target, including those on the street and in patrol cars.’

I then told him that I was at Danny Carver’s house in Streatham.

‘What in God’s name are you doing there?’

‘I came to ask him some questions.’

‘But you’re not—’

‘Just listen, guv,’ I cut in. ‘You need to get here as quickly as you can. And bring someone who’s computer savvy.’

‘Why? What’s going on?’

‘I think I know who the assassin is,’ I said.

‘Jesus. Have you got a name?’

‘Not as such. But it looks like she’s a well-known killer and was imported from Mexico to do the job for Slack.’

‘How did you find this out?’

‘I went on Carver’s computer.’

‘But his computer is with forensics.’

‘He has more than one, guv. And he keeps this one in a secret little room that wasn’t found during a search of the house.’

‘Holy shit. Give me the address and I’ll get there as soon as I can.’

Drummond turned up at Carver’s house fifteen minutes later along with a bunch of uniformed officers.

By then I had taken steps to protect myself against accusations of assault. I’d put the knife back in the drawer, removed my belt, which I’d used to hog-tie him, and made up a story about what had happened here.