Once you visit the Isle of the Dead, there's no hope of returning to the land of the living. A small island off the coast of Greece holds a secret so dreadful that once you step onto its soil you must remain there forever. General Pherides (master of horror Boris Karloff) is one such a visitor. Going to the island to honor the grave of his late wife, Pherides discovers that it's held in the grip of a terrifying plague -- a sickness that enters the victim's mind and drives them insane! Pherides leads the fight against the plague, but then falls prey to it himself. In his delirium, he believes that a woman named Thea (Ellen Drew) is a vrykolaka -- a vampire responsible for the deaths. Insanity runs rampant, and grave robbery, premature burial and ghastly vampires are the unspeakable horrors that await on the Isle of the Dead.