Théo Luther is the most formidable group leader of the Paris Criminal Brigade. After tracking down a child killer for many months, he becomes depressed and puts his marriage in jeopardy. Today, reintegrated into his unit, Theo is under surveillance. To be fully rehabilitated, he will have to overcome both his intimate demons and the criminals. His first investigation leads him to Alice whom he suspects of the murder of his parents. Unable to prove his guilt, he rages in front of this young woman who openly taunts him... From now on, Luther fights the worst assassins of Greater Paris under the gaze of a killer who seems to be - however - the only one to understand him.