A frightened child witnesses an intruder break into a cabin and steal the corpse of a recently dead relative. Terrified, she flees and comes face to face with Baron Victor Frankenstein, (portrayed by Peter Cushing). The body snatcher carries the body to Frankenstein’s secret laboratory, and a local priest, James Maxwell, discovers the theft. The young witness identifies both the thief and his employer, forcing Victor and his loyal helper away from town. They make for the Baron's hometown, Karlstaad, aiming to fund their next experiments by selling valuables taken from the abandoned Frankenstein chateau. There, they rescue Rena, a deaf-mute young woman, Tracy Stratford, from a gang of would‑be harassers and bring her to safety in their makeshift camp.
But the original plan hinges on returning to the chateau, only to find all the valuables have vanished. They retreat, and the following day Victor and his companion attempt to blend into a local carnival to remain inconspicuous. While in a nearby pub, Victor notices the burgomaster wearing one of his prized items—a ring—sparking a tense chase that ends with authorities recognizing him and forcing a hasty retreat. He hides at the exhibit of Zoltan, a hypnotist who has been banished from Karlstaad for lacking a license to perform. The hypnotist, Peter Woodthorpe as Zoltan, is drawn into Victor’s plan after a deft bit of psychological manipulation.
Zoltan agrees to reanimate the creature’s mind, though his ambitions are far from purely scientific. The reanimated being, the Monster, Kiwi Kingston at his command, helps Zoltan carry out robberies and exact revenge on the town’s authorities. Victor evicts Zoltan when he realizes the man’s true motives, but Zoltan cannot escape his own trap: he orders the creature to kill Victor, yet the creature turns on Zoltan instead. A wild rage seizes the experiment, and it shoots through the laboratory, eventually setting it ablaze. Hans escapes with Rena, and the two watch as smoke spills from the chateau.
In a final, devastating sequence, the creature goes berserk inside the lab as flames climb; the entire structure topples toward the cliff, sealing Victor’s fate along with the creature he sought to birth. The ensuing explosion marks the end of the perilous partnership and the peril it unleashed on Karlstaad, leaving behind a chilling reminder of ambition untempered by caution and a town forever haunted by what was brought back to life.
