Four police officers of the SDPJ Hauts-de-Seine, Eddie Caplan, Walter Morlighem, Theo Wachevski and Roxane Delgado have their lives turned upside down when their colleague, Max, committed suicide, following a case in which he is unfairly blamed. They then cross the "yellow line", not hesitating to circumvent the law to achieve their purposes in order to wash the honor of their friend Max.