The film begins when a stranger arrives in town. He takes quickly to his former mistress, Denise, who is happily married to John, and has an affair with his identiske twin brother Peter. They plan together to drive John crazy. After unsuccessful attempts to blackmail the couple receive the stranger, Gert, to help them with their evil plan.
Larry Ward
as Peter / John
Teresa Gimpera
as Denise
Giacomo Rossi Stuart
as Gert Muller
Silvana Venturelli
as Annie
Fernando Sánchez Polack
as Comisario
Eugenio Navarro
as Dr. Durán
Javier de Rivera
as Dr. Hernández
José Bastida
as Peter / John (set ups)