Le tueur du lac - Season 1 (2017)

After their first operation fails, the cops and paramilitary police take the risk of setting a new trap for the killer by using Marina, an officer on Clovis' team, as bait. Living with Lise's mother Marianne becomes unbearable at home, a situation worsened by the couple's relationship crisis since Lise has been doubting her husband's honesty. She continues her research and discovers the existence of another woman named Mathilde. Clovis is leading a double life.

The killer takes two new victims: Monica, a young woman, and Yacine, a fellow officer and friend of Clovis. For Lise, it's high time Clovis explained himself. Who is this woman Mathilde, who claims she lives with Clovis and is the mother of his child? Incapable of responding, Clovis leaves home and takes up temporary residence at police quarters. Faced with the new murders, the prosecutor decides to appoint a superior police officer to oversee the lake killer case. It doesn't take Diane Varella long to suspect that someone on Clovis' or Lise's team must be leaking ...

It's time for the truth to be told. Clovis confesses a deep secret to Lise, who learns about the dark side of his past. Meanwhile, as new chief of investigation Varella follows leads to find the suspected leaker in the police force, she gathers troubling information about one of the agents on the case.

Clovis is questioned by Varella at police headquarters. Lise and her team try to gather evidence to prove he is not guilty. They begin to suspect Lise's psychotherapist, Alexis Geller; Lise has been confiding in him since the beginning of the investigation. As Lise's mother Marianne slips into a coma after trying to commit suicide by drowning, Varella gets violently assaulted by the killer.

Laure, the neighbor, discovers disturbing facts about her husband and demands explanations. Lise, Clovis and their teams learn that Varella has disappeared. They suspect she has been abducted by the lake killer. They follow a lead that brings them to a hideout, where they find Varella's lifeless body. They are right on the verge of catching the killer.