Now the threat went beyond the organised crime task force. All police officers in London were potential targets, and there didn’t seem to be a damn thing we could do to stop it.

It was an alarming change of strategy aimed at ‘teaching you all a lesson’. It also illustrated yet again the startling ease with which a crazy person with a weapon can strike terror across a whole city or country.

We’d had it before, many times, with jihadists who let off bombs and attacked innocent people with knives. Now it was the turn of an assassin who was doing it, not for some radical cause, but because the gangster paying her wanted revenge on an entire police force.

I’d spent the last hour sitting on the sofa trying to work up the courage to go and confront the man I believed was heavily involved in what was happening. And to use brute force if necessary to get him to come clean.

I kept asking myself how I would feel if I chickened out now and another officer was killed tonight or tomorrow. Or what if the bitch came looking for me again? Or even went to the hospital to finish Aidan off?

It was entirely possible that Danny Carver was actually in touch with the woman. That he was the middleman between her and Slack. And if so, then maybe, just maybe, I could get to her through him.

Weighed against that were the dire consequences for me if it went belly up, like it had for Tony Marsden and his crew.

Anxiety clawed at my chest as I agonised over it. I started pacing up and down the length of the living room, clutching the sheet of paper with Carver’s address on it.

Once again images cascaded through my mind. Images with unwelcome clarity that were driving me towards committing a criminal act. Aidan in that hospital bed. Dave Prentiss lying dead in his own hallway. Marion Nash’s body on the floor of her shop. And the blood that poured out of me into the toilet pan as my own baby’s life was extinguished.

When the phone rang the acid churned in my stomach. I thought it might be one of the police bodyguards, ringing to see where I’d gone to without them.

But it was my mother, and I spent five minutes reassuring her that I was fine. She sounded terrified, though, and I yearned to reach out and give her a hug.

‘When will this end, Laura?’ she sobbed. ‘Surely it can’t go on. It’s so awful and sad. Why can’t the police stop it?’

‘We’re trying, Mum,’ I said. ‘Believe me we are.’

I told her where I was and gave her an update on Aidan’s condition, then said I’d contact her first thing in the morning.