Paris, in the 1960s. A series of crimes troubles the public tranquility. On March, 22, 1968, Hélène Picard, a prostitute sentenced to death two years before for several murders, is killed by executioner Louis Guilbeau. Immediately, the violent crimes, similar to Hélènes ones, go on again. In parallel, Louis is having an affair with the police woman in charge of the investigation... What are the obscure relations hidden behind the executioner and the mysterious killer? Who is this dark man in reality?