The snow is melting in the Swiss Alps and reveals the body of a woman murdered in a macabre staging near the French border; as Captain Sterenn Peiry starts investigating the case, she faces a personal crisis that could prove dangerous.

Sterenn decides to cover up her son's accident by reproducing the stagings of the serial killer she is tracking; her investigation progresses with Lyes Bouaouni from the French Police and Mélinda's absence gets noticed by her colleagues.

The noose is tightening around Sterenn's secret; Jérémy, who is the prime suspect, is summoned by the police and questioned by Lyes; temporarily removed from the investigation, Sterenn manages to uncover the link between the serial killer's victims.

Matteo, Jérémy's boss, is kidnapped by the serial killer and a race to save him begins; Sterenn faces the serial killer and tries to convince him to spare Matteo's life; the serial killer will only communicate with Sterenn, imposing a pact.

Sterenn has only a few hours left to honor the killer's pact if she wants to save her son; as for Lyes, he is convinced that Mélinda is not one of the killer's victims and has growing suspicions about Jérémy; desperate, Sterenn changes strategy.

While the pact with the serial killer is still ongoing, Lyes manages to convince the Swiss police that Sterenn is covering up for Jérémy and the homicide he committed; the police go after Sterenn and Jérémy.