I’d met Marion Nash on several occasions. And her husband had never tired of telling the rest of us how she had given up her job as a librarian to open her own bookshop. Her only son had flown the nest so she had put her heart and soul into making it a success.

Her death was indeed a terrible, pointless tragedy. The second in less than twenty-four hours. That in itself was enough to make the blood curdle.

It told us that we were dealing with a cold, calculating killer. A true professional. Someone who planned ahead. Someone who researched his victims and knew where they would be at any given time.

I thought it sensible to assume that the assassin was male. Most contract killers were, certainly in this part of the world. In South America and Mexico it was different. There women were just as likely to be gang leaders and hired guns.

But in Europe and the US it was a male-dominated profession. Some hitmen even advertised their services on the dark web. Many of those were rank amateurs, though, and they were often hired by men and women who wanted their spouses or business partners bumped off. They usually ended up getting caught and their subsequent trials were becoming regular features in tabloid newspapers.

But the real pros managed to ply their trade for years while raking in huge amounts of money. They were the guys who crime lords like Roy Slack turned to when they wanted one or more executions to be carried out cleanly and efficiently. They were like ghosts who appeared only when they were summoned and then disappeared again after their work was done.

It was possible that the killer now on the rampage in London had been brought in from abroad. If so then it was doubtful that he had ever appeared on the radars of any of our law enforcement agencies.

It would therefore be difficult, if not impossible, to identify him. So the only way we stood a chance of catching the bastard was if he made a mistake.

And how likely was that?

Before leaving the office, the Commissioner assured everyone that a plan would be drawn up to provide protection for all of us. But he reiterated what he had announced publicly – that the task force operations would not be suspended.

‘We cannot give in to this lunatic’s demand,’ he said. ‘If we do there’s no telling what will happen. He might well turn his attention to one of the other task forces or specialist units. Would we then be expected to close those down as well?’

It was a point I hadn’t considered because I’d been assuming that the motive for the threats and the murders was simply to halt our investigation into Roy Slack’s firm. If there was more to it than that then I couldn’t for the life of me think what it could be.