An American writer, Sam Dalmas (Tony Musante), is living in Rome with his girlfriend, Julia (Suzy Kendall). While visiting an art gallery, Sam witnesses an unsuccessful murder attempt by a mysterious figure. As the assailant is believed to be an infamous serial killer, Sam quickly becomes a key witness in the ongoing police investigation. After he begins searching for clues that may help him identify the killer, Sam discovers that he may be the next intended victim.