Joseph Losey's turbulent melodrama concerns a phony writer, Tyvian Jones (Stanley Baker), who has recently sold the film rights to his autobiography as a Welsh coal miner (actually penned by his deceased brother). Tyvian is engaged to Francesca (Virna Lisi), an alluring screenwriter, but then Eva (Jeanne Moreau) walks into his life.
Eva and her lover had sought shelter from a thunderstorm in his apartment and Tyvian is immediately attracted to her. He follows her to Rome, where Eva demands an elaborate hotel suite, tons of gambling money, and a bonus for sexual favors. When Tyvian assents in gratifying her wishes, Eva just laughs at him.
Tyvian then has to rush back to Francesca, since they are going to be married. But Tyvian forsakes her on their honeymoon and takes up with Eva again. Finding Tyvian and Eva together, Francesca is heartbroken and she commits suicide. After the funeral, Tyvian sets his sights on killing Eva, but, when he sees her, he finds that he is still obsessed with her.