L'Avventura (1960)

A group of rich Italians head out on a yachting trip to a deserted volcanic island in the Mediterranean. When they are about to leave the island, they find Anna, the main character up to this point, has gone missing. Sandro, Anna's boyfriend, and Claudia, Anna's friend, try without success to find her. While looking for the missing friend, Claudia and Sandro develop an attraction for each other. When they get back to land, they continue the search with no success. Sandro and Claudia proceed to become lovers, and all but forget about the missing Anna.