Dr. Frankenstein and his monster both turn out to be alive, not killed as previously believed. Dr. Frankenstein wants to get out of the evil experiment business, but when a mad scientist, Dr. Pretorius, kidnaps his wife, Dr. Frankenstein agrees to help him create a new creature, a woman, to be the companion of the monster.
Mary Shelley (Elsa Lanchester), author of Frankenstein, or The Modern Prometheus, reveals to Percy Shelley (Douglas Walton) and Lord Byron (Gavin Gordon) that Henry Frankenstein (Colin Clive) and his Monster (Boris Karloff) did not die. Both lived, and went on to even stranger misadventures than before.We flashback to scenes from Frankenstein (1931) (1931), which lead up to our new story. After the mill collapses, and it seems the Monster has been destroyed, the burgomeister (E.E. Clive) urges everyone to return to their homes. But the father (Reginald Barlow) of the little girl whom the Monster had killed (accidentally) in the first film, wants to see the creature's dead body with his own eyes before he can have peace. His wife (Mary Gordon) tries to stop him; but when the man wanders through the still-burning debris, he falls through a hole that leads to a flooded cavern below the mill. The Monster rises out of the water and kills the poor man, later doing the same for his wife. The Frankensteins' hysterical servant Minnie (Una O'Connor) also meets with the Monster, but manages to escape with her life. But no one believes her when she screeches that the Monster is still on the loose.Henry wants nothing more than to settle into a peaceful life with his new bride (Valerie Hobson). But his old professor, the sinister Dr. Pretorius (Ernest Thesiger), now disgraced, appears unexpectedly and convinces him to continue his work of creating new life. Pretorius has been conducting his own experiments but can do no better than to create people who are a few inches tall.Soon the village learns that the Monster is still alive. They capture him, but the powerful creature escapes his prison and goes wandering through the forest as the villagers hunt him.The Monster discovers an isolated cabin occupied by an old blind hermit (O.P. Heggie) who is playing the violin. The creature and the lonely hermit soon become friends, as the old man teaches the Monster the joys of music, cigars, bread and wine. The Monster understands human speech and soon learns to speak himself. They've both finally found happiness, which is dashed when two travelers stop by to ask directions. They recognize the Monster and attack him, inadvertently burning down the hermit's cabin in the battle. The Monster runs away, miserable once again.A chance meeting in a tomb brings Dr. Pretorius and the Monster together; and Pretorius uses the Monster to kidnap Mrs. Frankenstein and blackmail Henry into returning to his castle and continuing his experiments. The Monster wants his creator to build him a friend; and Pretorius wants to see dead tissue become a living woman. Henry is forced to give his creature a bride.Henry and Pretorius succeed in following the creation of Man with the creation of Woman (Elsa Lanchester again). But Woman is not happy with Man and backs away from him, hissing in horror and fear. The Monster is despondent. He frees Henry and his wife, and then releases a lever that blows the castle to atoms, thus destroying himself, his bride and Dr. Pretorius.Well, not quite. In the next film, Son of Frankenstein (1939) (1939), we learn that the Monster has managed to survive yet again.