While swimming in a lake in the Eastern Townships, Kate McDougall makes the macabre discovery of the corpse of a nine-year-old girl. Strong head, this former investigator of major crimes of the SQ, fired for insubordination, is initially suspected. But when other victims of the same age are found, the machiavellian work of a serial killer, nicknamed by the media the "Lake Monster", is confirmed. She who has been demoted to the region to deal with minor offenses is now catapulted into the most difficult investigation of her career. Immersed in this infernal spiral, Kate gives free rein to her demons, alcohol and sex, and will face her painful past to unmask the culprit. The series is an adaptation of Johanne Seymour's successful novel Le Cri du cerf.