Pilot James "Mac" McCarthy goes off course somewhere between Cuba and Puerto Rico and is unable to pick up any radio transmissions. When he and his passengers, Bill Summers and his black valet, Jefferson Jackson, hear a lone transmission in a foreign language, they crash land the plane on the island below. The lost men discover themselves in a graveyard, and follow the sound of drums to a nearby mansion. There they are greeted by Viennese Dr. Sangre, who treats Mac's minor head wound with the warning that untreated injuries are easy prey for evil spirits. Sangre says there are no radios on the island and allows the men to spend the night as his guests, although he insists that Jeff stay in the servants quarters in the basement. Jeff becomes alarmed when the maid, Samantha, and the cook, Tahama, call forth two "zombies," but when he runs upstairs to tell his boss, Sangre dismisses the idea as ludicrous. Sangre's wife Alyce also appears to be in a trance-like state, which Sangre attributes to jungle fever. Sangre appears surprised when Bill tells him about American Admiral Wainwright, whose plane disappeared in the same location. Sangre then tells the men that no one in his family, which includes his beautiful niece, Barbara Winslow, can leave the island because they are Austrian refugees lacking passports. Later that night, Jeff confides in Samantha that Bill is a government agent on a secret mission. Sangre's butler, Momba, Samantha and Tahama leave Jeff alone in the kitchen just before midnight, with the admonition not to pay notice to anything unusual. When two zombies nearly attack Jeff, he runs to Bill and Mac's room for safety. Jeff is later awakened by the appearance of a woman who seems to come and go through a wall, and when he awakens Bill and Mac, they believe him only after finding an earring. The three men split up to search the house, and Bill finds Barbara in the library reading a book on hypnotism. Barbara says that she is reading the book to help her aunt, who has been in the trance-like state since arriving at the island, and Bill confides his belief that Sangre is hiding a radio. Bill and Mac finally believe Jeff's stories about zombies after Mac is attacked by one. The next morning, Mac and Bill discover a freshly dug grave in the cemetery, and that someone has stolen the plane's radio. Mac goes in search of a generator, while Bill returns to the house, unaware that the admiral is being held hostage in a cellar and that Tahama is trying to pry military secrets from him with the use of voodoo. After Sangre calls in a report to his German allies, Mac disappears. Sangre then lures Jeff into the cellar, where he hypnotizes him into believing that he is a zombie. While Bill is searching for Mac, he finds Barbara using hypnotism on her aunt, and assumes that she is collaborating with Sangre, despite her protests that she is trying to restore her aunt's memory. Mac returns in a zombie-like state, and a physician called by Sangre says that he has been dead for hours. When Momba receives orders by radio for Sangre to transmit the stolen military information, he and Tahama prepare a special ceremony to wrest the information from the admiral. Jeff lines up with the other zombies for dinner, but Samantha breaks his spell. Jeff then meets with Bill and moments later, they hear a woman's scream and find Alyce dead. Bill and Jeff follow the sound of drums into the cellar, where Sangre is holding a ceremony during which the admiral's thoughts are to be transmitted into Barbara's brain. Bill breaks up the ceremony and when Sangre orders the zombies to attack Bill, they instead follow Mac, and turn on Sangre. Sangre shoots Mac and, while backing away from the zombies, falls to his death into a firepit. After Wainwright phones the Coast Guard, and Mac's injuries are treated, Wainwright tells Bill that Sangre forced his plane to land with a false radio signal, then killed his crew and tortured him for Canal Zone fortification plans. When his torture did not work, he used Alyce and Barbara as test subjects with other methods.