The police of police isn't done with the Departmental Service of the Judicial Police (SDPJ) group. The investigation into Caplan's group and Bernardi is led by a devious cop: Chief Superintendent Henri Brabant. For his part, Walter is still enraged about the violent aggression his children suffered. Behind Caplan's back, he enlists Wassim Alcala, an old friend from the army, to find Charlie (Caplan's mysterious friend who appeared in season 3) to equip him which what he needs to take down the Turks.