After recovering from injuries sustained in the mob attack upon himself and his creation, Dr. Frankenstein (Colin Clive) falls under the control of his former mentor, Dr. Pretorius (Ernest Thesiger), who insists the now-chastened doctor resume his experiments in creating new life. Meanwhile, the Monster (Boris Karloff) remains on the run from those who wish to destroy him without understanding that his intentions are generally good despite his lack of socialization and self-control.

The dashing, mysterious Count Dracula (Bela Lugosi), after hypnotizing a British soldier, Renfield (Dwight Frye), into his mindless slave, travels to London and takes up residence in an old castle. Soon Dracula begins to wreak havoc, sucking the blood of young women and turning them into vampires. When he sets his sights on Mina (Helen Chandler), the daughter of a prominent doctor, vampire-hunter Van Helsing (Edward Van Sloan) is enlisted to put a stop to the count's never-ending bloodlust.