It starts when Desire Rosenkvist of Stockholm Police receives a letter. Two things are immediately clear: the letter she holds in her hands was written in a state of utter desperation and paranoia. And it contains details of one of her old murder cases, which only the murderer could know. Desire contacts private investigator Sam Berger, who sets off to the remote north of Sweden with his colleague Molly Blom to find the author of the letter and to stop them in their tracks. But someone wants to keep them from getting to the bottom of the mystery at any cost and is watching their every move. What happens when the cops become the prey?