On New Year's Day, a wealthy family is found slaughtered inside their exclusive gated community in north London, their youngest child stolen away. The murder weapon is a gun for stunning cattle, leading Detective Max Wolfe to a dusty corner of Scotland Yard's Black Museum devoted to a killer who thirty years ago was known as the Slaughter Man. But the Slaughter Man is now old and dying.
The first message sent to Tom Thorne's phone was just a picture - the blurred image of a man's face, but Thorne had seen enough dead bodies to know that the man was no longer alive. But who was he? Who sent the photograph? And why? While the technical experts attempt to trace the sender, Thorne searches the bulletins for a reported death that matches the photograph. Then another picture arrives.