The frightening Boris Karloff 60s thriller with Karloff as a demented doctor using torture for scientific experiments.

Near the end of the 19th century, Prof. John Mayer and his assistant, the scientist Dr. Isabel Reed, accidentally invent a powerful ray. An alien travels to Earth to destroy the machine since it would be a threat to the universe. He initially possesses the mind of Thomas, a sex maniac and serial killer, to get close to Mayer during the demonstration of the machine to scientists and the military. Mayer's niece, Laura, meets an acquaintance of her uncle, the chemist Dr. Paul Rosten, and Mayer invites him to join the research. When Thomas gets close to Mayer, the alien also possesses his mind in order to destroy the device and his notes. Meanwhile, Thomas is not able to control his murderous impulses and attacks several women with a straight razor.

In Sierra Negra, graverobbers Barraza and Mendoza steal the coffin of Count Karol de Lavud, before heading to a hospital. Barraza sees a medallion upon the coffin's opening and demands more money from Mendoza. Meanwhile, Marta González, recovering from traumatic events, works as a nurse with Dr. Saldívar. When Barraza removes the wooden stake in order to steal Lavud's medallion, the vampire returns to life and begins a crime spree, hunting down Marta to marry her.

A scientist experimenting with past lives finds a reincarnated Aztec who can lead him to lost treasure—and to a creature that should remain lost. (Composed of footage from two unrelated Mexican horror films, LA CASA DEL TERROR and LA MOMIA AZTECA, plus new American-made footage.)