A thirty-four-year-old psychologist with a troubled past, Siri Bergman works in central Stockholm and lives alone in an isolated cottage outside the city. Terrified of the dark, she leaves all the lights on when she goes to bed—after having a few glasses of wine to calm her nerves—but she can’t shake the feeling that someone is spying on her through the blackened windows. When the lifeless body of Sara Matteus—a young patient of Siri’s with a history of drug addiction and sexual abuse—is found floating in the water near the cottage, Siri can no longer deny that someone is out there, watching her and waiting. With the help of Markus, the young policeman investigating Sara’s death; Vijay, an old friend and psychology professor; and Aina, her best friend, Siri sets out to catch the murderer and finally put her past to rest. But as their investigation unfolds, virtually everyone Siri trusts will become a potential suspect.