À double tour

“An intruder in the life of a family...was she really guileless?”

The mistress of the wealthy Henri Marcoux (Jacques Dacqmine) is found murdered, and his household names the milkman as the killer. Laszlo Kovacs (Jean-Paul Belmondo), the fiancé of Marcoux's daughter, doesn't believe it, and he starts asking questions in a family that would rather he didn't. Claude Chabrol, shooting his first film in colour, follows Laszlo as he looks harder at the people closest to him.