Luigi Muscati (Ron Nummi) is a successful man. He is engaged to Cinzia (Simona Borioni), a girl from a wealthy family, and his career is about to step forward thanks to a very profitable business he's dealing with. During a visit to Naples, he meets his young cousin Sonia (Vittoria Belvedere). No longer the little girl he played with as a child, she has blossomed into a sensuous and provocative young woman. On his return home, Sonia turns up on his doorstep needing a place to stay and he invites her to live with him. From that moment Luigi's life is transformed from one of quiet stability to insane passion as Luigi falls hopelessly in love with Sonia.