In a village of the Bavarian Alps, a young scientist named Henry Frankenstein and his assistant Fritz, a hunchback, piece together a human body. Some of the parts are stolen from freshly buried bodies in a cemetery, and some come from the bodies of recently hanged criminals. In a laboratory he’s built inside an abandoned watchtower, Frankenstein desires to create a human, giving this body life through electrical devices he has perfected. But he still needs a brain for his creation. At a nearby school, Henry’s former teacher Dr. Waldman still teaches, showing his class the brain of an average human being and the corrupted brain of a criminal so that they can compare the two. Frankenstein sends Fritz to steal the healthy brain from Waldman’s class during the night. But Fritz accidentally drops and damages it, and so brings Frankenstein the corrupt brain instead.
Henry’s fiancée Elizabeth speaks with their friend Victor Moritz about the scientist’s increasingly peculiar actions and how he secludes himself. Elizabeth and Victor ask Dr. Waldman for help in understanding Henry’s new behavior and Waldman reveals he is aware Dr. Frankenstein wishes to create life. Concerned for Henry, they arrive at the lab just as the scientist makes his final preparations, the still lifeless body now ready on an operating table. As a storm rages outside, Henry Frankenstein claims he has now discovered the energy that brought life into the world and invites Elizabeth and the others to watch his great experiment. With a pulley system, Frankenstein and Fritz raise the operating table high in the room, moving it toward an opening at the top of the tower. The creature and Frankenstein’s equipment are exposed to the lightning storm and empowered. The hand of Frankenstein’s creature begins to move. The scientist triumphantly shouts, ‘It’s alive!’
Frankenstein’s Monster, despite its grotesque form, seems to be an innocent, child-like creation. Dr. Frankenstein welcomes it into his laboratory and asks his creation to sit, which it does. He then opens up the roof, causing the Monster to reach out towards the sunlight. Fritz enters with a flaming torch, which frightens the Monster. Its fright is mistaken by Frankenstein and Waldman as an attempt to attack them, and it is chained in the dungeon. Thinking that it is not fit for society and will wreak havoc at any chance, they leave the Monster locked up, where Fritz antagonizes it with a torch. As Henry and Waldman consider the Monster’s fate, they hear a shriek from the dungeon. Frankenstein and Waldman run down and find that the Monster has strangled Fritz. The Monster lunges at the two but they escape, locking the Monster inside. Realizing that the Monster must be destroyed, Henry prepares an injection of a powerful drug and the two conspire to release the Monster and inject it as it attacks. When the door is unlocked the Monster lunges at Frankenstein as Waldman injects the drug into the Monster’s back. The Monster falls to the floor unconscious.
Henry collapses from exhaustion, and Elizabeth and Henry’s father arrive and take him home. Henry is worried about the Monster but Waldman reassures him that he will destroy it. Later, Henry is at home, recovered and preparing for his wedding while Waldman examines the Monster . As he is preparing to vivisect it, the Monster awakens and strangles him. It escapes from the tower and wanders through the landscape. It has a short encounter with a farmer’s young daughter, Maria. She is not afraid of him and asks him to play a game with her in which they toss flowers into a lake and watch them float. The Monster enjoys the game, but when they run out of flowers he thinks Maria will float as well, so he throws her into the lake where, to his puzzlement, she disappears beneath the surface. Upset by this outcome, the Monster runs away.
With preparations for the wedding completed, Henry is serenely happy with Elizabeth. They are to marry as soon as Waldman arrives. However, Victor rushes in, saying that Doctor Waldman has been found strangled. Henry suspects the Monster. Meanwhile, the Monster enters Elizabeth’s room, causing her to scream. When the searchers arrive, they find Elizabeth unconscious on the bed. The Monster has escaped.
Maria’s father arrives, carrying his drowned daughter’s body. He says she was murdered, and the villagers form a search party to capture the Monster and bring it to justice, dead or alive. In order to search the whole country for the Monster, they split into three groups: Ludwig leads the first group into the woods, Henry leads the second group into the mountains, and the Burgomaster leads the third group by the lake. During the search, Henry becomes separated from the group and is discovered by the Monster, who attacks him. The Monster knocks Henry unconscious and carries him off to an old mill. The peasants hear his cries and they regroup to follow. They find the Monster has climbed to the top, dragging Henry with him. The Monster hurls the scientist to the ground. His fall is broken by the vanes of the windmill, saving his life. Some of the villagers hurry him to his home while the rest of the mob set the windmill ablaze, with the Monster trapped inside.
At Castle Frankenstein, Frankenstein’s father, Baron Frankenstein, celebrates the wedding of his recovered son with a toast to a future grandchild.