Once again Paula ape woman (Vicky Lane) is brought back to life, this time by a mad doctor (Otto Kruger) and his disfigured assistant (Rondo Hatton), who also kidnaps a nurse in order to have a female blood donor. By this time, Paula's been brain damaged by experiences in the last film, so there's not much for her to do except wander around.

Dr. Stendahl, a biochemist, performs a series of reanimation experiments on rabbits using electronic charges and blood transfusions. Much to the amazement of his secretary, Ann Forrester, and medical student, Don Young, Stendahl is finally able to restore life to a once-deceased animal. That night, Moloch, a deformed brute, arrives at the city morgue with a note requesting the release of Paula Dupree's body, a hybrid creature better known as The Ape Woman. When Fred, the attendant, states that he must call the police first, Moloch strangles him, then steals the body and a morgue ambulance. After placing Paula's body in his wagon, Moloch drives the stolen vehicle off a cliff and heads off to an isolated country house. The next day, police inspector W. L. Harrigan of the homicide squad visits Stendahl's medical office, as a surgical smock was found near the crash scene and laundry marks indicate that it belonged to Don. Harrigan questions the medical student about his whereabouts that evening, but the newly engaged Don and Ann state that they were together all night. Later, Stendahl asks Ann to run an errand with him, and the two soon arrive at the country house. The mad scientist then exposes himself as the mastermind behind the theft of Paula's body and pronounces his intention to use a blood transfusion from Ann to bring the Ape Woman back to life. As a concerned Moloch watches, Stendahl nearly kills Ann during the medical procedure, but is successful in reanimating Paula. Still unaware of how to return Paula to her human form, Stendahl sends Moloch to steal the medical records of Dr. Sigmund Walters and Dr. Carl Fletcher, the physicians who had previously brought Paula back from the dead. The next morning, a concerned Don questions Stendahl about Ann's disappearance, only to have Harrigan arrive at the medical office and accuse him of murder. Later, with Walters and Fletcher's research in hand, Stendahl uses some of Ann's glandular secretions to change Paula back into her beautiful human form. Unfortunately, the Ape Woman's brain has been damaged, so the mad scientist decides to transplant Ann's brain into Paula's head. Meanwhile, Harrigan questions Dan about Stendahl's research, leading the police inspector to suspect the biochemist of the murders. With Stendahl in town doing research for the upcoming operation, Paula manages to escape her imprisonment and wanders into the nearby woods. Moloch then goes to Stendahl's medical office to inform the scientist of her escape, at which time Don recognizes his fraternity pin, which he had given Ann in lieu of an engagement ring, on Moloch's lapel. Don follows the disfigured man to the country home, but is soon captured by Stendahl. After a brief escape, Don is tied up and forced to watch as Stendahl prepares to begin the brain surgery. When Don informs Moloch that the operation will mean Ann's death, the brute becomes enraged and attacks Stendahl. The mad scientist is then forced to shoot and kill Moloch. Stendahl is soon killed himself, however, as Paula, having transformed back into the Ape Woman, rises from the operating table and strangles him. The Ape Woman then heads for Ann with the same intent, but Harrigan arrives in time and shoots her. With the case solved, Harrigan releases Ann and Don from their bonds, and the couple looks forward to a happy future together.