Léna, 28, community manager, has just joined the communications department of the Paris police headquarters, which is looking to modernize its image. Paris is under tension, a serial killer is raging in the capital and is destabilizing the police using social networks.

Léna, through her knowledge of social networks, allows Commissioner Ruffin's team to save a new victim in extremis. After new exchanges with the killer, she begins to understand the treasure hunt set up to discover the place and day of his next crime.

Léna puts herself in more and more danger by interacting with the killer. He threatens her loved ones, plays on her nerves. The situation turns against her. She becomes a suspect in the eyes of the police... What if the killer wanted to trap her?