The corpses of two women are found – one right after the other – in the lakeside town of Annecy, and married police officers Lise and Clovis have no doubt that it must be the work of a serial killer.

The police find a third corpse in a state of decomposition at Annecy. Could the woman, who was assassinated using the same ritual as the other two victims, have been the killer’s first target?

Lise asks her mother Marianne to come and live with her family. As the killer continues to ensnare women, Clovis and Lise’s teams work hard to understand his operating methods and attempt to trap him.

The police take the risk of setting a new trap for the killer using an officer on Clovis’s team as bait. Lise’s research makes her doubt her husband’s honesty. Has Clovis been leading a double life?