Abbott and Costello, as railroad baggage clerks, receive a strange shipment the last remains of Dracula and Frankenstein's monster. But this deadly duo is still very much alive. So when the shipment arrives at the House of Horrors, the Monsters are not in their crates but have disappeared to a secret hideaway island. Blamed for the disappearance, Abbott and Costello follow their trail to the island, where not only do they meet up with Dracula (Bela Lugosi) and the Monster (Glenn Strange), but a Mad Scientist (Charles Bradstreet) who wants to switch Costello's brain with that of the Monster. With everyone chasing each other, the Wolf Man (Lon Chaney, Jr.) shows up to scare them all. In the end, everything works out: Costello finds romance and the Monsters find their final resting places...or do they?