A child witnesses an intruder steal the corpse of one of her recently dead relatives. Terrified, the child flees from the cabin where she is hiding. Running through the forest, a hand reaches out to her. The girl screams and runs away. The figure is revealed to be Baron Victor Frankenstein.
The body-snatcher takes the corpse to Frankenstein's secret laboratory. The Baron tells his assistant, Hans, to pay the man. When the body-snatcher asks what he'll do with the body, Frankenstein says he intends to cut out the deceased man's heart, remarking; "He won't be needing it".
Meanwhile, a local priest discovers the theft and is morally outraged. The young child of the deceased who witnessed the theft identifies both the body-snatcher and his employer. The priest angrily confronts each in turn, and interrupts Frankenstein's attempt to restore life to the heart, smashing vital equipment in the lab. Forced to leave town because of their experiments, Frankenstein and Hans return to the Baron's hometown of Karlstaad, where they plan to sell valuables from the abandoned Frankenstein chateau to fund new work. Nearing the village, the pair nearly run over a wild haired, deaf-mute young woman, who is being accosted by a couple of thugs. Hans tries to help her, but she flees to the hills. The men find a festival is in progress and are able to pass through the village unquestioned.
Upon their arrival, the chateau is found to have been apparently looted by the locals and the laboratory appears to be in ruins. As Hans pours the Baron a drink, Frankenstein recounts to Hans the events that led to his exile:
Ten years prior, he had brought a being to life. While reasonably functional in most aspects, the creature would eat nothing but fresh, raw meat and wantonly killed local livestock, eating their entrails. A police constable and some farmers encountered the creature with Frankenstein in the woods, and shot at both of them. Frankenstein suffered a grazed arm, the monster a non-lethal head wound. Baron Frankenstein was arrested, while the creature escaped to a nearby mountain. (He is seen falling into a crevice after the sound of another gunshot.) Frankenstein was briefly imprisoned, charged with assault of a police officer and having committed acts of heresy. He was fined and exiled, since up to that point the creature had not caused any human harm. The flashback sequence ends with the Baron lamenting the destruction of things humanity doesn't understand (a theme he repeats throughout the film).
The following day, the Baron and Hans enter Karlstaad for a meal, donning festival masks as a precaution. They enter a crowded inn and place an order. While waiting, Frankenstein spies the corrupt Burgomeister wearing one of his rings and is outraged, causing a scene which forces a hasty departure. The authorities have now recognised him, so the Baron flees with Hans through the village festival, eventually hiding at the hypnotist, Zoltan's, exhibit. The arrogant Zoltan clashes with the police and is arrested, covering the escape of Frankenstein and Hans.
Later that evening, Frankenstein bursts into the Burgomeister's apartments, again outraged at finding the corrupt official has largely stolen for himself Frankenstein's "confiscated" valuables. During his tirade, the police (led by the constable who had originally shot the creature – now the Chief of Police) breaks in to arrest the Baron. Frankenstein manages to escape. He and Hans retreat to the mountains where they again encounter the deaf girl. She leads them to her makeshift shelter in a cave to avoid an impending storm and soon, all go to sleep.
Sometime later, the waif awakens and skulks off, awakening Frankenstein. Curious, he searches through the cave and finds his original creation frozen inside a glacier. Calling Hans, they build a fire; thaw the creature out; carry it down the mountainside to the chateau; and restore it to life. However, the creature's brain, while functioning, will not respond to commands. Frankenstein, desperate to restore active consciousness to his creation, comes up with the idea of obtaining the services of Zoltan, the hypnotist, to reanimate the creature's mind. Zoltan has been banished from Karlstaad for not having a license to perform. After clever psychological manipulation by the Baron, he agrees to the task.
Zoltan is successful but has less than scientific interests at heart. With the monster responding only to his commands, Zoltan uses the creature to rob and take revenge upon the town's authorities. Frankenstein evicts Zoltan, who then instructs the creature to attack Frankenstein. He wards off the monster's attack with an oil lamp, frightening the monster. The creature in turn brutally kills Zoltan, who is blocking the creature's path.
The creature quickly goes into a fit of violent rage. The Baron orders Hans to get the girl out of the room while he tries to confront his creation. In the middle of its rampage, the monster rips apart the electrical components which had been used to resurrect it, causing a fire to break out in the laboratory. Frankenstein tries to give the creature a dose of chloroform to subdue it, but it drinks it instead. Disgusted and poisoned, the creature stumbles, knocking over bottles of flammable liquids and causing a switch to short-circuit and explode into flames.
Hans asks the Baron if he can hear him, but Frankenstein orders Hans to get away from the place while he tries to shift the rubble blocking the doorway. The creature stumbles about in terror of the surrounding flames. Realizing that there is no other way out, the Baron grabs a chain and launches himself into the midst of the inferno in a desperate attempt to find another exit.
From a distance, the villagers see Hans and the girl fleeing from the chateau. They look back to see black smoke pouring out from the tower where the laboratory is. Suddenly there is an explosion and half of the tower is thrown over the edge of the cliff. Seeing this, Hans murmurs to himself that; "They beat you after all"...
The fate of Baron Frankenstein is unknown.Peter Cushing as Baron Victor Frankenstein
Peter Woodthorpe as Zoltan
Duncan Lamont as Chief of Police
Sandor Elès as Hans
Katy Wild as Rena the Beggar Girl
David Hutcheson as Burgomaster of Karlstaad
James Maxwell as Priest
Howard Goorney as Drunk
Anthony Blackshaw as Policeman
David Conville as Policeman
Caron Gardner as Burgomaster's Wife
Kiwi Kingston as the Creature
Additional American release castSteven Geray as Dr.Sergado
Patrick Horganas David Carrell
Maria Palmer as Rena's mother
William Phipps as Rena's father
Tracy Stratford Rena as a child
The film breaks continuity from the preceding film, The Revenge of Frankenstein. Denis Meikle described the break: "Any pretext of a connection to The Revenge of Frankenstein is dispensed with in a brazen display of contempt for continuity. A flashback creates a prior history that is wholly unrelated to the last Sangster script and is instead plundered from Universal's Frankenstein Meets the Wolfman."
For the U.S. television release there were additional scenes featuring characters that didn't appear in the original film and have no interaction with the main characters. Patrick Horgan plays a reporter who questions a doctor (Steven Geray) about Baron Frankenstein. There are also scenes of the deaf-mute girl (Tracy Stratford) and her parents (Maria Palmer and William Phipps), none of whom ever appear in the film again.
Allmovie's review of the film was mixed to negative, calling it "dismal" and "the worst of Hammer Films' Frankenstein series". Other reviews have been more merciful in their reception. The film currently holds a three star rating (6/10) on IMDb and an average 50% on Rotten Tomatoes.
In North America, the film was released on 6 September 2005 along with seven other Hammer horror films on the 2-DVD set The Hammer Horror Series (ASIN: B0009X770O), which is part of MCA-Universal's Franchise Collection, with two films per each side of the discs. In 2015, the set was released as a 4-DVD set putting two films per disc due to major glitches the original set had. This set was re-released on Blu-ray on 13 September 2016.