À la Folie on AllMovie

A menage-a-trois between rival sisters and a boyfriend provide the dramatic focus of this French film. The sisters Alice and Elsa have been apart for two years. Alice, a painter, lives in Paris with her lover Franc. Problems for the happy couple ensue when Elsa suddenly appears at their door after leaving her cheating husband and two children. Elsa immediately begins trying to dominate their lives. Alice wants the out-of-control Elsa to leave, but then suddenly changes her mind. To thank her, Elsa destroys her art studio, has sex with Franc, convinces him that Alice is unbalanced, and then ties Alice up in her apartment.