The BBC News Channel was the first to break the story. A young female presenter suddenly adopted a solemn expression and said, ‘We’re getting reports that a police officer has been shot dead in London. He hasn’t yet been named, but we understand he was at home in Battersea with his wife when he was gunned down on his doorstep.’

Roy Slack had been glued to the TV screen since Rosa had called him an hour ago to inform him that she’d claimed her first victim.

‘It’s done,’ she’d said, her voice clipped and devoid of emotion. ‘Tune into the news for the details.’

And that was all she had said before hanging up.

While waiting for the story to appear, Slack had phoned Danny to get him to send another message to the detectives. After telling him what to put in it he’d poured himself another Scotch and lit one of his Cuban cigars.

Now he sat with his feet up on the coffee table and savoured the warm sense of satisfaction that washed through him. His mission was properly underway now and there was no turning back.

For him revenge had always been sweet, but this time it was going to be sweeter than ever. Those smug, self-righteous detectives who were coming after him were going to pay for the sins of all those who’d gone before them.

And he was going to relish their suffering and the turmoil it was going to create.

Killing Hugh Wallis would never have been enough. This wasn’t about individuals. Wallis had been sent to Terry’s house by those above him, so they were just as culpable. And so were the slags who had covered up the crime by concluding that Terry was responsible for his own death.

It was just another example of the rank hypocrisy that prevailed inside the Met. As far as he was concerned Scotland Yard was a swamp filled with vermin. The coppers who weren’t corrupt were guided by a sickening sense of moral superiority. They were obsessed with bringing down villains who provided services that were much in demand. But they spent far less time and effort going after rapists, muggers, wife beaters, child molesters and jihadist fanatics who infested the capital.

Men like Harry Fuller did not deserve to go to prison for thirty years while paedophiles were as a rule sentenced to less than half that.

Slack’s own father had died in prison after he was stitched up by coppers who planted a gun in his car. They did it because they knew he was part of an armed gang that robbed a jewellers, but hadn’t been able to prove it. Ryan Slack, who was just fifty-four, was three months into his sentence when he got into a fight and suffered a fatal stab wound.