Drummond’s phone was stuck to his ear so we didn’t get a chance to talk. He had conversations with various people, including the Commissioner and the commanding officer at Wandsworth, on whose patch the killing had taken place.

The murder of any police officer always sparks a wave of disquiet. But what had happened to Dave Prentiss was going to have massive implications for the Met and indeed for the country.

It sounded like he was the victim of a cold-blooded assassination, and gut instinct was telling me that it was committed by, or on behalf of, the person who sent us the death threat.

I didn’t believe that it was a coincidence, and I gathered from what Drummond was telling everyone that he didn’t either.

I had never seen him so rattled, but that was understandable. Prentiss was one of twenty detectives under his command and we’d all received the same text message warning us to stop working for the task force.

I feared now that it was indeed just the start … that there would be more murders if we didn’t yield to the demand.

And that our close friends and family members would be among the victims.

The street was filled with police cars, and their flashing lights were reflected in the windows of the small terraced houses.

I’d never been to Prentiss’s house before and when we pulled up outside it my first thought was how nice it was. But then the sight of all the uniforms on the driveway hit me like a cattle prod and robbed me of air. As I stepped out of the car onto the pavement I felt an icy chill in my stomach.

Drummond came and stood beside me and asked me if I was all right.

‘Not really, guv,’ I said. ‘But I’m glad I’m here. I need to see this.’

He was about to say something else when a tall man in a white forensic suit appeared and introduced himself as DCI Bob Resnick. He looked about fifty and had dark, wavy hair.

‘I was told that you were coming, sir,’ he said to Drummond. ‘I understand that Dave Prentiss was on your task force.’

‘That’s right,’ Drummond said. ‘So what have you got?’

He told us what we already knew, that Prentiss had been shot dead when he opened his front door to someone.

‘His wife was upstairs with her new baby when the doorbell rang,’ he said. ‘She said her husband went to answer it. She didn’t even know he’d been murdered until she came downstairs a couple of minutes later to see why he wasn’t responding to her calls. She found him in the hallway.’

‘Did she not hear the shots?’ Drummond asked.