In this unconventional French drama, a group of unnamed aristocrats interact at a palatial château, resulting in an enigmatic tale told partially in flashback. X (Giorgio Albertazzi) is convinced that he has met the beautiful A (Delphine Seyrig) before in the Czech resort town of Marienbad, and implies they had a romantic relationship. M (Sacha Pitoeff), who may be A's husband or boyfriend, confronts her mysterious suitor, leading to conflict and questions about the truth behind his story.