In 1995, seventeen-year-old Tatiana mysteriously disappears near the Perpignan train station, leaving her family in anguish and confusion. Three years later, in 1998, the mutilated body of a young woman, Leïla, is found near the same station. Flore, a young investigator, joins the judicial police team and faces her first homicide case. Tatiana's mother, Marie-José, has embarked in a relentless quest to find her daughter, while the police team, led by Vidal and Sabueso, works to track down the killer. The connection between the two cases remains tenuous, but an unsettling figure begins to draw their suspicion.

As the investigation into Leïla's murder intensifies, Vidal's team focuses their efforts on Olivio Palomyno, a doctor with strange behavior. During their surveillance of the suspect, the officers uncover increasingly disturbing clues. Flore, the new recruit, who suffered a brutal assault during a hazing ritual, hesitates to file a complaint against her colleague. Meanwhile, Marie-José, tormented by the disappearance of her daughter three years earlier, continues her solitary search, exploring increasingly surprising leads.

Olivio Palomyno is held in custody and interrogated as the prime suspect in Leïla's murder. While he has been the main lead for months, the investigation takes a turn when another young woman disappears under troubling circumstances. This development forces the investigators to question their assumptions. Flore, shaken but determined, finds her footing within the team despite ongoing tensions. Meanwhile, Marie-José grows closer to the family of Marianne, the second victim. With a predator still active and elusive, the team is aware that time is running out to prevent further tragedies.

As the world prepares to enter the year 2000, the investigation stalls, plunging the team into doubt. To assist them, a controversial profiler is sent from Paris. However, his extravagant theories complicate the investigators' work even further, sowing discord and distress within the team. Flore, weakened by a recent assault, channels her anger and throws herself fully into the case. Meanwhile, Tatiana’s family fluctuates between hope and despair. Vidal grows increasingly distant from his wife and daughter.

The investigators race against time to arrest a new suspect. However, his confessions raise more questions than answers. Nora's body is found, but the investigation remains mired in uncertainties about the other victims. Determined to close the case despite the setbacks, Flore gradually establishes herself as the pillar of the team while Vidal, exhausted by years of pursuit, considers stepping down.

After sixteen years of investigation, the team finally manages to arrest the perpetrator of two of the murders thanks to a DNA match. During a grueling interrogation, Flore, with Vidal's help, forces the suspect to confess to the murders of Leïla and Marianne. Despite the victory, Flore remains haunted by the unanswered questions, particularly regarding the disappearance of Tatiana.