Somewhere in Western-Central Europe in the 1860s, a trio of grave robbers, led by a man named Lynch (Herbert Fux), deliver a corpse to Baron Frankenstein (Joseph Cotten) and his assistant Dr. Marshall (Paul Müller), for obvious reanimation purposes.
Baron Frankenstein's daughter Tania (Rosalba Neri) arrives from school, having completed her studies in medicine, and is greeted by her father and his young servant, the handsome but mildly retarded Thomas (Marino Masé). Tania reveals to her father that she has always understood his work with "animal transplants" to be a cover for his work reanimating corpses, and that she intends to follow in his footsteps and help him in his work.
The next day, Frankenstein, Tania, and Marshall witness the execution of a criminal who is hanged down a well, Frankenstein and Marshall both have an eye toward harvesting the criminal's body for their experimentation. Law enforcement agent Captain Harris (Mickey Hargitay) arrives to harass Lynch at the hanging. Harris claims to be on to Lynch's grave robbing.
That evening, having harvested salient body parts, Frankenstein and Marshall successfully reanimate a gruesome giant corpse with a scarred, misshapen head (Peter Whiteman) as Tania secretly watches. Almost instantly, however, this monster bear-hugs Frankenstein to death - breaking his back - then walks out of the castle. Tania and Marshall report the murder to Harris, but claim that it was a burglar. Harris points out that according their description, the burglar would be over seven feet tall.
The monster, roaming the countryside, comes across a couple having sex out in the open, and after scaring away the man, picks up the woman, who screams and then faints. The monster then carries her later body and drops it into a river, and when the body is later found by two men, the monster kills one by breaking his neck. After Harris questions Lynch, and Lynch refuses Tania's offer for more grave-robbing work, the monster breaks into Lynch's home while he is having sex with a local whore, and kills Lynch by beating him to death. The monster then kills a local farmer and his wife, and Lynch's two grave-robbing friends.
Tania then goads Marshall into admitting harboring romantic feelings for her. She responds to his affections, but says that while Marshall's body is old, she finds the body of Thomas young and attractive. The "solution" to this situation will be to transplant Marshall's brilliant brain into the brain-damaged Thomas's young healthy body. To accomplish this, Tania seduces Thomas into having sex while Marshall secretly watches, and Marshall kills him with a pillow during their lovemaking.
Tania then successfully transplants Marshall's brain into Thomas's body. Thomas now speaks with Marshall's voice and his body has become inhumanly strong as well. Meanwhile, Frankenstein's monster has continued to terrorize the town, and the local villagers, having had enough, arrive with torches and pitchforks before following the monster to the castle. In the chaos, the monster returns, knocks down Harris, and has a fight with Marshall/Thomas, who cuts off his arm. When the monster bear-hugs Marshall/Thomas, Tania stabs him in the back with a sword, and Marshall/Thomas kills him by puncturing his head open with a metal hand tool. The monster is defeated, but Tania has made it clear that she has no allegiance to Marshall.
The villagers storm into the castle and set it aflame in the hopes of killing the monster. Harris arrives with Thomas's sister Julia (Renate Kasché) to see Tania and Marshall/Thomas naked and enjoying post-fight sexual intercourse as the castle burns beside them. However, during their lovemaking, Marshall/Thomas chokes Tania to death as the flames of the fire consumes them.Rosalba Neri as Tania Frankenstein (credited as Sara Bay)
Joseph Cotten as Baron Frankenstein
Paul Muller as Dr. Charles Marshall
Peter Whiteman as The Creature
Herbert Fux as Tom Lynch, the graverobber
Mickey Hargitay as Captain Harris
Lorenzo Terzon as Harris' assistant (credited as Lawrence Tilden)
Marino Masé as Thomas Stack (uncredited), the mildly retarded servant
Renate Kasché, as Julia Stack (credited as Renata Cash), Thomas' Sister
The film was largely financed through Harry Cushing, but just prior to the start of filming a letter of credit from a film company was not accepted by the Italian banks. The final last-minute $90,000 needed to make the film was obtained from Roger Corman's New World Pictures. The suggestion of Rosalba Neri for the lead role was from one of the financers of the film.
In his analysis of the film, Louis Paul described the film as "a hybrid of the '70s Hammer horror films' infatuation with nudity and sadism and the golden age of Italian horror's gothic period."
The film is often compared with the Frankenstein cycle made by the Hammer Studios (1957–72), and may also have been an influence on Paul Morrissey's controversial Flesh for Frankenstein (1973).
Some have posited that Di Lorenzo intended that this film should present a feminist slant to the mad scientist genre.
The film was also the second movie lampooned on MSTing show Incognito Cinema Warriors XP in 2008.