When an heiress vanishes on a remote island, her best friend and fiance search for her.

A group of wealthy, jaded Italian socialites are the members of a yachting party cruising off the northeast coast of Sicily. Included in the small group are Sandro, a 40-year-old architect who has long since abandoned his artistic principles for a life of easy commercial success; Anna, Sandro's mistress, who is dissatisfied with their almost purely sexual relationship; and Claudia, Anna's friend, who is the one member of the party unaccustomed to a life of wealth. They go ashore to explore a barren, volcanic island. Following a sudden storm, it is discovered that Anna has disappeared. A search of the island proves fruitless, and Claudia blames Anna's apparent suicide on Sandro's heartlessness. Separately, and then together, however, Claudia and Sandro visit places on the mainland where a strange girl is said to have been seen. Gradually, as it becomes more and more apparent that Anna is not going to be found, Claudia and Sandro turn to each other. Though she at first resists his advances, her feelings of shame and guilt are overcome by her passion, and she becomes his mistress. Later, the two lovers rejoin their friends at a party in an elegant hotel in Taormina. That night Claudia awakens to find Sandro gone. She prowls through the hotel until she discovers him clumsily making love to a high-class prostitute. As Claudia stares at him, Sandro realizes the uselessness and emptiness of his actions. Filled with despair, he wanders out into the cold, gray dawn and begins to sob quietly. Claudia follows him and, feeling compassion and desolation, places her hands on his shoulders and wordlessly forgives him.