It seemed to last for an interminably long time, although she found out later that the film was only seven minutes and twenty seconds long, and it involved the killer doing other things to his victim, terrible sexual things that she recalled from the autopsy reports. And throughout it all there was not a single glimpse of him, not even a gloved hand at the end of the hammer. Even in the midst of his bloodlust he was being careful and controlled in his actions, and when he’d finished, and what was left of Adrienne Menzies was no longer moving, the camera shut off abruptly. Just like that.

Tina swallowed hard, and for a number of seconds continued to stare at the blank screen, conscious of how hard and fast her heart was beating — a thought that made her feel ashamed. Beside her, she could hear DCI MacLeod’s laboured breathing. Then he stepped forward and shut the laptop’s lid, as if by doing so he could shut out the horror they’d just witnessed.

‘Good God,’ he said quietly. ‘What drives some people?’

There was no answer to this. All Tina knew for sure was that she’d met far too many of them in her police career, and the crimes they committed never got any easier to handle. More than once in recent months, her parents and brother, still reeling from the fact that she’d killed a man in the line of duty, and even more horrified that she’d joined the team tasked with tracking down a serial killer, had suggested that her job was doing her more harm than good. They were almost certainly right, yet Tina was capable neither of leaving the career that she seemed to love and loathe in equal measure, nor of coping with its constant pressures.

‘The hammer looked like the one we found at Kent’s place, didn’t it?’ she said at last.