In the middle of a wild rave party, the body of a 78-year-old man is discovered among the crowd, beaten and stabbed. There's no way to trace the identity of this elderly man. Darius and his colleagues are left in a state of incomprehension: what was he doing there? And why didn't anyone seem to have seen him during the party? While Marijo finds a strange piece of paper in the victim's jacket lining, we then discover Françoise, her husband, and their best friend. They're all between 75 and 84 years old. Their common thread: a general sense of fed-upness. Their pensions are ridiculous, they feel like they've become a burden on society, and they're slowly dying. Their plan? To rob a supermarket.

The body of an unidentified man, wearing jogging gear, is left brain-dead on the steps of the Lille University Hospital. There's no trace of who left him. The only clue: a gray van, spotted on surveillance cameras. On the Invisibles brigade's side, the clues are slim, but they identify the jogger. A bad guy, according to many people. While things are getting tense at Duchesse and Ben's, an IGPN cop arrives to monitor the Invisibles group, who are in the line of fire of the hierarchy... Elsewhere, we discover little Stella, seriously ill. Stella is worried: her father is acting increasingly strange and tense. Besides, what does he do with his days, locked in the annex at the bottom of the garden?

The body of a mutilated woman is found along a road. For the Invisibles brigade, the killer's relentlessness and madness are beyond doubt. While Duchess begins to have doubts about her ability to cross paths with Ben on a daily basis, she crosses paths with the handsome Alexis, an old acquaintance... Darius, for his part, confronts Chistera about Leïla, his adoptive sister. He understands that she is in grave danger, in a high-stakes criminal case. At the same time, we discover two fiber optic installers who are making the rounds of Lille homes. While one is flirtatious and insistent with the women he meets, the other is more reserved, shy... What's the connection?

Two bodies entwined, cast in concrete. This is the strange crime scene our Invisibles find themselves at. All except Duchess, who has joined her family to attend her cousin Laeticia's wedding. While the team discovers that these two young people without identities have nothing to do with each other, Duchess realizes that her uncle is hiding something within the castle where the entire family is gathered. While nothing seems to connect these two stories, Ben and Marijo will soon make a discovery that will change everything. Darius, for his part, tries to help Leïla, who doesn't seem to see the trap set by Chistera, which is closing in on her.

The corpse of a woman, horribly mutilated. The crime scene shocks our investigators. It's clearly the work of a psychopath... Who seems to be Hamel, a young man suffering from mental illness and nightmarish visions... which are those of the crime scene! Hamel, who confides in his psychiatrist, is quickly arrested following a second, similar murder. Too easy? At least, that's Marijo's opinion, who sets off on another lead, one that could affect her much more than she thinks. At the same time, she's worried about Darius, like Ben and Duchess. Darius seems to have completely lost his mind. And they're not wrong: to save his sister, he'll commit the irreparable... and risk paying a high price for it...