Erotic Blackmail (1974)

Original title: Le corps a ses raisons

From the darkest underbelly of European erotic cinema comes this seedy tale of a couple whose pleasures involves swinging with other couples, money and blackmail. When Hugo and Valerie invite Max and Dauphine over for a short vacation in the country, they do not realize that they are being played by the couple. But there are more people that want to join in the fun. Etienne and his friend Julien do not accept any longer to just watch as silent bystanders from the outside in: they want to be in the midst of the action. Therefore, once alone in the villa, they take advantage of the situation and attack Valerie and Dauphine while both their husbands are absent. But who's the really victim and who's playing who?