The movie starts with the Frankenstein children, little nine-year- old Monica (Nicoletta Elmi
) and her brother, Erik (Marco Liofredi
), playing dissection with a doll. When they are through taking its guts out, Erik, with Monica's approval, chops its head off with a miniature guillotine.
We next see the children in the company of their mother, Baroness Katrin Frankenstein (Monique van Vooren
) as she brings them home after removing them from a school she no longer approves of. On the way the Baroness observes shepherds Nicholas (Joe Dallesandro
) and Sacha (Srdjan Zelenovic
). She chides Nicholas for neglecting his work as he sports with a peasant girl.
At home her complaints to Baron Frankenstein (Udo Kier
) - who is both her brother and her husband - are ignored as he is too busy working on his laboratory project. In the lab he is laboring with Otto (Arno Juerging
), his assistant, to create a pair of super-humans by literally piecing together the best body parts they can find. The Baron believes that if he can bring these creatures to life and get them to mate, he can create a race of superior beings only obedient to his commands. The girl creature (Dalila Di Lazzaro
) who is lying naked on a table in his lab is almost finished, but the Baron needs a head for his male creation. The Baron is not only concerned with creating living beings, but making ultimately beautiful ones, so he wants to find a male head with a Serbian nose.
That night as the maid (Liù Bosisio
) serves the family dinner, the Frankensteins argue. The Baroness does not know what to do with the children now they have been taken out of school so the Baron suggests she take them on a picnic. Despite scoffing at this idea, the next day she leads the children into the country-side where she again runs into Nicholas romantically involved with a girl. She scolds him and tells him to report to her at the castle the next morning.
Later that day, Nicholas kids his friend Sacha about his desire to be a monk and his lack of interest in girls. He manages to convince Sacha to go with him that night to the local brothel for some fun, though Sacha appears to agree to go along only to make Nicholas happy.
The Baron tests out his female creation by making love to it while Otto watches. The Baron has the rather strange fetish of reaching inside her stitches and fondling her gallbladder as the does it.
The Baron has determined that in order to ensure the creatures will mate the male must have a large sexual appetite. To select a brain with this characteristic, Otto and he wait outside the brothel that night. They can tell from the sounds there is such a man inside, but they misidentify that man as Sasha (who has the Serbian nose the Baron wants), instead of Nicholas. As Sasha and a drunken Nicholas make their way home that night they are set upon by the Baron and Otto. Nicholas is knocked out and Sasha beheaded. The Baron and his assistant then take their prize back to the lab.
The next morning Nicholas awakes and finds Sasha's headless body. He buries him and decides it is time to leave town. Before he does, however, he stops at the castle to keep his appointment with the Baroness. She convinces him instead to stay and become the new stable boy and her secret lover.
With Sasha's head on the male's body the Baron's work nears completion. Despite the fact that they do not eat solid food or talk much, he decides to bring his creations to the family dinner table that night. Nicholas, who is serving dinner, is appalled to find his friend's head now attached to a much taller body and decides something sinister must be happening in the Baron's lab.
The maid is also snooping around the lab and is caught by Otto who proceeds to chase her down and rape her. When he tries to fondle her gallbladder, as the Baron enjoys doing, however, he accidentally kills her.
With the children's help Nicholas sneaks into the lab and observes the Baron's first attempt to mate his creations. Despite ordering the female creature to kiss the male multiple times, the male does not respond and the Baron is furious.
Nicholas then goes to the Baroness to warn her about the Baron's work and is surprised when she comes to the Baron's defense. She tells Nicholas not to bother the Baron. She beleives Nicholas's only function at the castle is to serve her sexual needs. At this he storms out of her bedroom in disgust.
The Baron is convinced that someone has been in his lab fooling with his work. He confronts his wife, who turns Nicholas in; in return for the Baron's promise to order the male monster to serve her sexual needs for two hours (She does not realize he is dud in the area). Later in her bedroom as she instructs the monster in pleasing her she tells him to hold her tight. He does this too much, however, and breaks her back, killing her.
In the lab, the Baron and Otto have caught Nicholas and have him hanging from a pulley by his wrists in mid-air. The Baron plans to use him to fix the male monster's libito problem. When the Baron is out of the room, however, Otto brags to Nicholas he is just as smart as the doctor and proceeds to demonstrate this by making love to the female creature while fondling her gallbladder. He fails to do it right and this kills her. The Baron returns to find the girl creature dead and in a rage strangles Otto.
The monster returns to the lab carrying the Baroness's body. At this new turn of events the Baron losses he temper again. He blames Nicholas for ruining his plans and gets a knife to kill him. Before the can commit the murder, however, the monster runs a pike through the Baron's back and out his belly. He dies.
Nicholas tells the monster to let him down so they can escape. The monster tells him he finds himself too horrible to live and commits suicide by tearing open his stitches and disembowing himself.
This leaves Nicholas hanging from the ceiling while the only two other people left alive in the castle - little Monica and Erik - enter the lab. Instead of freeing Nicholas, however, they pick up large scalpels and we are given the eerie feeling the dissection scene at the beginning of the film is about to be repeated with Nicholas taking the place of the doll. The screen fades to black.