The marquis Galeazzo di Torre Alta is murdered by a mysterious killer who calls himself Diabolicus. His heirs are his three brothers and a sister, but all of them, with the exception of Monsignor Antonino di Torre Alta, are killed by Diabolicus. The police are unable to solve the case, but when Antonino gives his inheritance to Pasquale Bonocore, illegitimate son of his father and Pasquale is in prison and therefore can't be the killer, all the clues are in the hand of the police.
Director: Steno
Story: Vittorio Metz, Roberto Gianviti
Screenplay: Vittorio Metz, Marcello Fondato, Bruno Corbucci, Giovanni Grimaldi, Roberto Gianviti
Director of Photography: Enzo Barboni
Producer: Gianni Buffardi
Galeazzo / Carlo / Scipione / Antonio / Laudomia / Pasquale
Barone Lallo
Donna Fiore
Commissario di polizia
Ispettore Scalarini
Notaio Cocozza
Detective Privato
Dottor Santoro