A serial killer is operating on both sides of the Franco-Swiss border. Captains Peiry from Switzerland and Bouanni from France investigate the macabre crimes. But the Swiss captain has problems of her own.
Melting snow reveals a woman's body. Her murder seems to have macabre aspects. Sterenn Peiry is put in charge of the case but crosses ethical boundaries to help her son, Jérémy.
Sterenn covers up for Jérémy. She also continues her investigation, together with French detective Lyes Bouaouni. Mélinda's absence is noticed.
The noose is tightening around Sterenn's secret. Lyes questions Jérémy. Sterenn uncovers the link between the serial killer's victims.
A race against the clock begins when the serial killer resorts to kidnapping. Sterenn tries to convince the killer to spare his victim's life. Where will this end?
Sterenn has only hours left to honour the pact if she wants to save her son. Lyes is convinced that Mélinda is not one of the serial killer's victims. So who killed her?
Lyes convinces the Swiss police that Sterenn is involved in a cover-up. Sterenn and Jérémy are both arrested, but the pact is still to be fulfilled.