In a European village, a young scientist, named Henry Frankenstein, and his assistant Fritz, a hunchback, piece together a human body, the parts of which have been collected from various sources. Frankenstein desires to create human life through electrical devices which he has perfected. Elizabeth, his fiancée, is worried over his peculiar actions. She cannot understand why he secludes himself in an abandoned watch tower, which he has equipped as a laboratory, refusing to see anyone. She and a friend, Victor Moritz, go to Dr. Waldman, Henry's old medical professor, and ask Waldman's help in reclaiming the young scientist from his experiments. Waldman tells them that Frankenstein has been working on creating life.
Elizabeth, intent on rescuing Frankenstein, arrives just as Henry is making his final tests. He tells them to watch, claiming to have discovered the ray that brought life into the world. They watch Frankenstein and the hunchback as they raise the dead creature on an operating table, high into the room, toward an opening at the top of the laboratory. Then a terrific crash of thunder, the crackling of Frankenstein's electric machines, and the hand of Frankenstein's monster begins to move, prompting Frankenstein to shout 'It's alive!'. Through the incompetence of Fritz, a criminal brain was secured for Frankenstein's experiments instead of the desired normal one. The manufactured monster, despite its grotesque form, initially appears to be a simple, innocent creation. 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 find the monster has strangled Fritz. The monster lunges at the two but they escape, locking the monster inside.
Realizing that the creature 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 creature lunges at Frankenstein as Waldman injects the drug into the creature's back. The monster falls to the floor unconscious. Henry leaves to prepare for his wedding while Waldman examines the creature. As he is preparing to dissect it, the creature 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, who 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 the monster thinks Maria will float as well, so he throws her into the lake and she drowns. Upset by this outcome, the monster runs away. With preparations for the wedding completed, Frankenstein is serenely happy with Elizabeth. They are to marry as soon as Waldman arrives. Victor rushes in, saying that the Doctor has been found strangled in his operating room. Frankenstein suspects the monster. A chilling scream convinces him that the monster is in the house. When the searchers arrive, they find Elizabeth unconscious on the bed. The monster has escaped. Maria's father arrives, carrying his daughter's body. He says she was murdered, and a band of peasants form a search party to capture the monster, and bring it to justice. In order to search the whole country for the monster, they split into three groups: Ludwig leads the first group into the woods, Frankenstein leads the second group into the mountains, and the Burgomaster leads the third group by the lake.
During the search, Frankenstein becomes separated from the group and is discovered by the monster, who attacks him. The monster knocks Frankenstein 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 Frankenstein 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, killing the entrapped monster inside. At Castle Frankenstein, Frankenstein's father, Baron Frankenstein celebrates the wedding of his recovered son with a toast to a future grandchild.