When the French police discover the blood-drained bodies of young women floating in the river Seine, journalist Pierre Lantin undertakes a personal investigation into the "Vampire Murders." His work is forever being interrupted by the unwanted advances of Gisele, the beautiful and wealthy niece of the Duchess du Grand--who, unbeknownst to him, is, in fact, the vampire ringleader of a criminal underground of mad scientists and re-animated corpses, devoted to keeping her forever young! Released in a heavily altered version in America as The Devil's Commandment, this pioneering shocker - acknowledged as the first genuine Italian horror film - is presented in its original European version.
When bodies are found floating in the River Seine, drained of blood, French police begin an investigation into these seeming "Vampire Murders." A curious journalist is drawn into the mystery as well, but is constantly distracted by the lovely Gisele, who is the niece of the Duchess du Grand. Back at the palace of the Duchess, a mad scientist is draining young women of their blood in order to keep the Duchess, a vampire ringleader, alive.