While running the vacuum cleaner at the police station one night, Morgane glimpses an ongoing investigation file, spots an error and can't resist the urge to correct it.

A man is taking a bath in a hotel room when a stranger in a mask forces his head and drowns him under the water. This is Morgane's first case as a consultant for Lille DIPJ, with Kadarec's disagreement. She was reluctant at first, but accepted the post, subject to the reopening of the investigation of Romain's, her boyfriend, disappearance, which Hazan supervises.

When two little girls disappear, everyone's suspicions turn to their father, a solitary and unstable man; a new lead regarding Romain's disappearance comes to light.

The body of a veterinarian is discovered at her clinic; everything seems to indicate death from natural causes, but Morgane suspects the young woman was poisoned.

With Romain's natural death confirmed, Morgane must go through her duel in reverse. Emilien Kerr is found in a parking lot, suffocated with a plastic bag.

A Lille football club supporter is found dead in the court's changing rooms; accompanied by her daughter, Thea, who is doing an internship at the police, Morgane sets out to investigate the male-dominated world of football fans.