On the night of 12 October 2016, a Grenoble police unit hosts a retirement party for their captain while celebrating the promotion of his younger replacement, Yohan Vivès. The mood is celebratory, but shadows linger as a major case brews on the outskirts of the celebration, hinting at a crime that will haunt the city.
Later that night, in Saint-Jean-de-Maurienne, 21-year-old Clara Royer says goodbye to her friends and leaves the house of her best friend Stéphanie “Nanie” Béguin Nanie. As she walks home in the dark, Clara is accosted by a masked assailant who calls her by her name before dousing her with lighter fluid and setting her on fire.
In the morning, Yohan Vivès and senior detective Marceau, assigned to the case, discover Clara’s charred body in a nearby park and notify her parents. When asked about Clara’s ex-boyfriends, Nanie mentions Wesley Fontana, a former co-worker at a bowling alley in La Toussuire. The next day, Yohan and a colleague, Loïc, question Wesley, who admits he was sexually involved with Clara but claims she kept pursuing him even though he had a girlfriend, who later confirms his alibi.
Marceau and Loïc question a contact found on Clara’s phone, Jules Leroy, who reveals that he had a casual sexual relationship with her and giggles while they discuss the way she was killed. Yohan questions Nanie again to divulge the names of Clara’s other ex-partners. One of them, Gabi Lacazette, is brought in for questioning and reveals that he wrote a rap song about setting Clara on fire after learning that she was unfaithful to him, though he insists that he is not a violent person.
At the police station, Yohan receives a disposable lighter delivered anonymously inside an envelope. One evening, Yohan and Marceau visit the crime scene, where they meet Denis Douet, an older man who tells them that he found the lighter nearby, while claiming to be one of Clara’s exes. The next day, Yohan questions Nanie yet again since she omitted Denis from the list of Clara’s partners. Nanie denies that Clara had sex with Denis and becomes upset with Yohan’s persistent questions about Clara’s relationships with men, tearfully declaring that she was killed because she was a girl.
Clara’s father finds a bloodied T-shirt at her makeshift memorial and hands it over to the detectives. The T-shirt belongs to Vincent Caron, who was convicted of domestic violence against his previous partner. During questioning, he admits that he also had an affair with Clara, while his live-in girlfriend Nathalie defends him and provides an alibi for him. After listening to tapped phone conversations in which Vincent is verbally abusive towards Nathalie, Marceau goes to his apartment and physically attacks him until Yohan arrives and intervenes. Marceau is subsequently transferred.
Nearly three years later, an investigating judge asks Yohan to reopen Clara’s case. Yohan expresses his frustration with the case, saying that although the killer has not been identified, he feels that all the men he questioned were capable of committing the crime. As the third anniversary of Clara’s murder approaches, the judge suggests that Yohan hide a camera in a fake gravestone at her grave, hoping that the culprit will expose himself.
Yohan and a new young recruit, Nadia, stake out Clara’s grave at night. The next day, they find that the footage shows an unidentified young man taking off his shirt and singing next to Clara’s grave at night. Nadia identifies the man as Mats, who created an online memorial for Clara. He is taken into custody, claiming to have met Clara at the Chambéry hospital. The detectives soon learn that Mats was admitted to the Chambéry psychiatric hospital at the time of the crime and that he became fixated on Clara after reading about her murder.
Disheartened, Yohan asks Nadia if she believes in ghosts, to which she replies that “the dead stay with us forever, and the important things we do are for them.” Yohan later writes Marceau an email saying that although Clara’s murder remains unsolved, he has high hopes for Nadia.
