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 that Anna has gone missing. Anna's boyfriend Sandro and friend Claudia try unsuccessfully to find her. While they are searching, 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.