A Fêmea do Mar (1981)

The lonely Jeruza lives in a simple isolated house by the seaside with the siblings Cassandra and Ulisses and the family survives by selling handicrafts for a local store. Her husband, Santiago, is a sailor who has been missing for many years. When the stranger Roque arrives at Jeruza's house late afternoon, he tells her that Santiago was murdered in a bar fight. Jeruza lodges Roque to spend the night and they have a one night stand. He then seduces Cassandra, who loses her virginity with him and he convinces Ulisses to have an incestuous relationship with his sister. Jeruza realizes that Roque, who has a dreadful secret, is a destructive being that is threatening her family.