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Claude Chabrol directs the tense psychological thriller Que la Bête Meure (This Man Must Die). When his young son is the victim of a hit-and-run car accident, writer Charles Thenier (Michel Duchaussoy) is determined to find the killer. Obsessed with avenging his son's death, he carefully records his thoughts in a diary. He travels to Paris and meets actress Helene Lanson (Caroline Cellier), who is a prime witness to the accident. After they start up a love affair, he discovers that the driver of the car was her brother-in-law, Paul Decourt (Jean Yanne). Paul also owns the auto repair shop that fixed up the car after the accident. Believing Paul is the killer, Charles befriends his son Phillipe Decourt (Marc Di Napoli). As it happens, Phillipe also wants Paul dead for his own reasons. Charles manages to get invited to the family's seaside home in Brittany in order to finally get his revenge, but things don't work out according to plan.