When a long-missing boy reappears in Stockholm, Detective Joona Linna realizes that a notorious serial killer’s reign of terror has not ended but has instead evolved through a dangerous accomplice. Linna must navigate a complex web of deception to locate the boy's sister, who remains captive under the control of the mysterious 'Sandman.' To extract information, he deploys Inspector Saga Bauer into a high-stakes undercover operation within a maximum-security psychiatric facility. The narrative follows a tense, multi-perspective structure that pits the psychological fortitude of the investigators against the calculated manipulation of a confined predator.

This novel is widely recognized as a quintessential entry in the Nordic Noir genre, noted for its relentless pacing and dark, atmospheric intensity. Critics and readers frequently highlight the authors' ability to maintain suspense through intricate plotting and the chilling psychological games played by the antagonist. The character of Saga Bauer is often cited as a compelling addition to the series, providing a necessary foil to the more seasoned Joona Linna. The narrative's focus on the psychological toll of the investigation ensures that the stakes remain high throughout the entire duration of the story.