A killer is cleaning up the streets of Milan by murdering those considered as deviant. An ornamental dragonfly, soaked in the blood of the victim, is left on each body.

Paul Naschy
as Inspector Scaporella

María Kosty
as Ingrid

Erika Blanc
as Silvana Scaporella

Ángel Aranda
as Pietro Volpini

Ricardo Merino
as Edmundo

Susana Mayo
as Claudia Volpini

Eduardo Calvo
as Professor Sandro Campitelli

Mariano Vidal Molina
as Police Commissioner

José Canalejas
as Ruggero

Ramón Centenero
as Vittorio Darucchi