So Sweet… So Perverse (1969)

Industrialist Jean is living a jet set life in late sixties Paris. Things are not so well at home with his frigid wife Danielle. He meets their new neighbour, Nicole, and they become lovers. But she has a sadistic ex-boyfriend, Klaus, which keeps showing up. It soon transpires that Danielle and Nicole are conspiring against Jean, Klaus being the hitman hired to murder him.