The Paris judicial police are investigating a serial killer who drugs his victims before cutting off their thumbs, and who steals their phones to post a final photo on social media after the fact.

Léna, a young intern who works in the communications department of the Paris police headquarters, alerts the judicial police officers after noticing that the account of Capucine de Warren, the most followed influencer in France, has just posted a photo that had already been posted a year earlier. The police rush to the young influencer's home and find her drugged and mutilated like the other victims but still alive.

In order to catch the culprit as quickly as possible, Commissioner Agathe Ruffin takes the risk of integrating Léna into her team in order to benefit from her knowledge of social media. Léna manages to communicate with the killer and get a clue about his next victim, but the ensuing police operation turns into a fiasco and leads to the humiliation of the police on social media.

From being a valuable collaborator, Léna becomes a suspect in the eyes of the commissioner and her police officers.