This Man Must Die(1969)
When his young son is killed in a hit and run accident, Charles Thenier resolves to hunt down and murder the killer. By chance, Thenier makes the acquaintance of an actress, HelĆØne Lanson, who was in the car at the time of the accident. He then meets HelĆØneās brother-in-law, Paul Decourt, a truly horrible individual.