Ben said nothing. He couldn’t speak. He just wanted to cram the tablet sideways between the stranger’s teeth and pound it in until it disappeared down his throat. But before he could react either way, a movement on the screen made him tense up even more. Because whoever had slipped unnoticed into Grace’s bedroom to film her hadn’t come alone. The second man who stepped out of the shadows the other side of the bed was clad all in black, head to toe, apart from the three pale ovals of the eye and mouth apertures of his balaclava. His hands were gloved. One of them held a semiautomatic pistol. That was black, too, like the long, tubular sound suppressor fitted to the end of its barrel.

The second man stepped up to the edge of the bed. Raised the muzzle of the silenced handgun a few inches from the back of Grace’s head, almost close enough to brush against her hair. He held it there for a few seconds as she went on sleeping, oblivious, as serene as a dormant child. Then he lowered the weapon, stepped away and melted back into the graininess of the shadows as though he’d never been there. With that, the video clip ended and the screen went black.

Ben knew how this game was played. What he’d just been shown was a classic textbook warning. A display of power. Telling him, See, this is what we can do. We can do it easily. We can do it any time. And nobody will even see us coming.

The stranger said, ‘Needless to say, she had no idea of what was happening. Around the time you were boarding your flight at Inverness, she was getting up and preparing to go off to work. That’s where she is now. Going about her police duties without the faintest clue that her every move is being monitored around the clock by a team of operatives ready to move in on command and execute their orders. Nor does she ever need to know, so long as you play your cards right and cooperate with me and my colleagues. I expect I have your attention now, don’t I?’

The trap had just sprung shut, with Ben neatly snared inside it. He said nothing.

The stranger went on: ‘Oh, you can play it cool if you like. But I’m sure you must be full of questions. For example, you’re probably wondering who I am. For the purposes of this conversation, you can call me Saunders. As to the rest, such as whom I work for and what interests I represent, that’s not your concern. You can simply rest assured that this is not a bluff, and that you need to take what I’m telling you with the utmost seriousness. Am I making myself clear?’

‘I think you’ve made your point,’ Ben said.