This movie starts with three men arrested for disorderly conduct at a dance. After they are released, they take a train trip, vent their continuing anger on a young Algerian, and kill the man by forcing him out of a window on the speeding train. Their crime is witnessed by Isabelle (Christine Pascal) and reported to the police, enabling commissioner Couturier (Roger Hanin) to find the killers. The major problem now is to prevent a race riot when right-wing extremists falsely accuse some North Africans of reprehensible actions and the townspeople gather to demonstrate at the prison.