The movie starts with the villagers of Frankenstein speaking of rumors that Ygor is still alive and that he is trying to revive the monster. Th
is rumor turns out to be true, and the villagers agree to demolish Castle Frankenstein to prevent the monster from returning. Little do they realize, but the explosions that are destroying the castle have released the monster from his sulfur tomb that had preserved him since the end of Son of Frankenstein. Ygor takes the Monster to Vasaria, where the second son of Henry Frankenstein, Ludwig Frankenstein (played by Sir Cedric Hardwicke) has a successful medical practice, along with his assistants, Dr. Kettering (played by Barton Yarborough) and Dr. Theodore Bohmer (Lionel Atwill).
What transpires is a series of events that leads to the monster being revived again and again causing problems for the residents of Frankenstein village and the Frankenstein family. A key event that convinced Ludwig Frankenstein to revive the monster was seeing the ghost of his father Henry Frankenstein (also played by Hardwicke), who tells Ludwig to "perfect his creation by fixing its brain."