Four cops of the SDPJ of the Hauts-de-Seine, Eddy Caplan, Walter Morlighem, Théo Wachevski and Roxane Delgado see their lives turned upside down when their chief, Rossi, commits suicide, following a case in which he is unjustly implicated. They then cross the "yellow line", not hesitating to circumvent the law to achieve their ends in order to clear their honor and that of their boss. Suspected of abusing a prisoner during an interrogation, Major Rossi Vogel is interviewed by the IGS. Placed in custody, he takes the only path that seems open to him.