While looking for an apartment, Jeanne (Maria Schneider), a beautiful young Parisienne, encounters a mysterious American expatriate Paul (Marlon Brando), mourning his wife's recent suicide.
Instantly the two are inexplicably drawn to each other and they embark on a stormy and passionate affair, in which they do not reveal their names to each other.
Their relationship deeply touches affects their lives, as Paul struggles with his wife's death and Jeanne prepares to marry her fiance, Tom, a film director making a cinema-verite documentary about her.