Experimenting in hypnotic regression to past lives, Dr. Edmund Redding of the Cowan Institute in Pasadena has discovered that Ann Taylor is a reincarnated Aztec woman. Via her recovered memories, she is able to lead Redding and his associates to a hidden chamber in the Great Pyramid of Yucatan, where they hope to find the lost treasure of the Aztecs. Instead, they find two mummified bodies - one of a modern man, quite dead, and the other of an ancient Aztec, quite alive. They are able to return safely to Pasadena with both finds, but a rival professor, Janney, kills Redding and steals the body of the modern man-mummy. This he subjects to a resurrection experiment, which works - only the mummy proves to be a werewolf. This creature breaks free of Janney's lab. Meanwhile, a hired thief sent by Janney to steal the other, living mummy, is overcome and that creature escapes also. Two supernatural menaces roam the city that night...