A human heart is discovered on the shores of the Loch, and forensic psychologist Blake Albrighton is brought in to join the investigating team. He quickly forms a disturbing theory about the motive behind the seemingly inexplicable murders, but Chief Inspector Frank Smilie is quick to dismiss his ideas. However, if the new arrival is correct, the once peaceful Highland community could be set to endure far more deaths, as a serial killer prowls the area.