Somewhere in Western-Central Europe in the 1860s, a trio of grave robbers led by Lynch [Herbert Fux] delivers a corpse to Baron Frankenstein [Joseph Cotten] and his assistant Dr. Marshall [Paul Müller] for obvious reanimation purposes. The scene sets a tense mood of ambition and danger, as the castle walls shelter a fascination with life beyond death and the people drawn into its dangerous orbit.
Baron Frankenstein's daughter, Tania [Rosalba Neri], arrives from school bearing new medical ambitions of her own. She reveals to her father that she has long understood his work with “animal transplants” to be a disguise for reviving corpses, and she vows to follow in his footsteps and help him push the boundaries of their experiments. The dynamic between father and daughter is marked by shared curiosity, tempered by the looming ethical murk of their methods, and Tania’s resolve signals a new (and perilous) collaboration.
The next day, Frankenstein, Tania, and Marshall witness the execution of a criminal who is hanged into a well. Captain Harris [Mickey Hargitay], a law enforcement agent, arrives to harass Lynch as the hanging proceeds, signaling that the town’s authorities are growing wary of the grave robbers’ activities. After the crowd disperses, the trio harvests salient body parts and moves forward with their attempt to reanimate the body. They succeed in bringing to life a grotesque giant—its scarred, misshapen head a stark banner of their experimental reach.
Tragically, the moment of triumph turns deadly when the towering monster bear-hugs Frankenstein to death, breaking his back, and then stalks away from the castle. Tania and Marshall report the murder to Harris but claim it was the work of a burglar. Harris notes that the description implies a creature over seven feet tall, a clue that deepens the sense of dread surrounding their creation.
The monster roams the countryside, clashing with the fragility of ordinary life. It interrupts a couple in an isolated moment, carries the terrified woman to a river, and later kills one man by breaking his neck when two others discover the body. Harris continues to chase leads, while Lynch’s own fate worsens: the monster breaks into Lynch’s home during a tryst with a local prostitute and kills Lynch, then proceeds to slaughter a local farmer and his wife, as well as Lynch’s two grave-robbing companions. The scale and brutality of the creature’s rampage push the town to the edge and set the stage for a deeper, more troubling plan.
Tania moves the plot toward catastrophe by pressing Marshall to admit romantic feelings for her. She makes it clear that while Marshall’s body is old, she finds Thomas’s body—his youth and vitality—more compelling. The solution is radical: transplant Marshall’s brilliant brain into the brain-damaged Thomas’s Young body. To make this work, Tania seduces Thomas into a sexual encounter while Marshall secretly watches; during their lovemaking, Marshall kills him with a pillow, clearing the way for the brain transplant.
The procedure is completed: Marshall’s brain now inhabits Thomas’s body, giving the man a new, almost superhuman strength and a voice that belongs to Marshall. The town’s terror, however, has only grown louder, as Frankenstein’s monster continues to terrorize the village. The villagers, armed with torches and pitchforks, converge on the castle, intent on ending the nightmare they believe the creature represents. In the ensuing chaos, the monster returns, knocks Harris aside, and fights Marshall/Thomas, who amputates the creature’s arm in the struggle.
As the Beast closes in, Tania makes a fatal choice and stabs it in the back with a sword. Marshall/Thomas then drives a metal hand tool into the creature’s head, finally killing it. The monster’s threat is crushed, but the cost is mounting: Tania’s allegiance remains volatile, and she shows no true loyalty to Marshall.
The villagers surge into the castle, setting the sprawling complex aflame in a desperate bid to end the nightmare. Harris arrives with Julia Black [Renate Kasché] to witness the scene—Tania and Marshall/Thomas, naked and engaged in post-fight intimacy, amid the glow of the burning fortress. Yet even as fire consumes the castle, the final moment reveals a tragic turn: Marshall/Thomas, in the throes of possession and power, begins to choke Tania as the flames rise around them, leaving their fate and the town’s future uncertain and ominous.
