Stephan, a shady Polish art dealer, is convicted of selling stolen artwork and is sentenced to prison for one year. Mado, his wife of uncertain nationality (possibly Creole), finding herself without any financial resources and at Stephan's urging, moves in to the apartment of H.J. Heider, a wealthy Englishman, and his wife Lois, a painter. H.J. has a history of inviting young women to move in to the "spare room" and with whom he then has sexual relations. Lois permits this arrangement because she wants to keep H.J. happy.

Most of the movie is a character study of the four principals. Mado visits Stephan in prison once a week, although both H.J. and Lois complain about it. Mado succumbs to H.J.'s advances, and it is unclear how much of it is willing and how much is not.

After Stephan is released from prison, he leaves France but does not take Mado with him.

Quartet is the story of a girl who, adrift with her feckless husband amidst the literati of glittering Paris in the 1920s, becomes entrapped by a rich and sybaritic English couple. Adapted from the wistful, melancholy autobiographical novel by Jean Rhys, Quartet is full of intense confrontations dazzlingly acted by Alan Bates, Maggie Smith, Anthony Higgins, and Isabelle Adjani. This is one of the Merchant Ivory team’s darkest and most compelling dramas of dangerously intertwined relationships.