Aliens who run a traveling circus revive a vampire, a werewolf, a mummy and Frankenstein's monster and plan to use them to take over the world. They intend to isolate the factor that makes these monsters so frightening to Earthlings and then create an army of such monsters. The werewolf they revive (Waldemar Daninsky, of course) saves the world by destroying the other monsters in hand-to-hand combat and ultimately blowing up the aliens' underground base.