An anonymous vigilante stalks the streets of Edinburgh. As his behaviour escalates, the police are at a loss, they can find no clues to his identity, and no trace of his whereabouts. DI Helen Birch has been told to stay away from the case but she’s never been one to play by the rules. When her colleague Amy comes to her asking for help, DI Birch finds it impossible to resist the challenge and soon, her life is on the line. Will she crack the case before it breaks her? Or has she finally met her match?