Scott Warrington returns to his childhood home in the Louisiana bayou at the urging of his old family doctor, Harvey Keating, who believes that Scott's sister Lila was poisoned to death. With Scott is private detective Larry Adams, and Larry's servant, Jeff. Larry poses as Scott, and vice versa, to protect Lila's brother, and together they visit Lila's bereaved husband, Von Altermann. Unknown to the visitors, Von Altermann has murdered Lila and through scientific experimentation, has turned her into a zombie. When Rosella, one of the maids, shows Jeff the other zombies working in the swamp, Jeff becomes terrified and reports back to Larry. They then go to make sure that Lila's body is still in the parlor, but unexpectedly find her walking through a doorway. Von Altermann denies the possibility that she is alive, and when he brings them back into the parlor, Lila is lying in her casket, and Von Altermann's secretary, Jennifer Rand, is appalled that they are behaving so strangely. Von Altermann secretly meets with a German agent in his laboratory, and reveals that he has successfully developed a method of turning the dead into zombies and bending them to his will. When the agent promises to return Von Altermann to his homeland, the scientist vows that he will provide Germany with an army of indomitable zombies with which to win the war. However, Von Altermann is surprised when his demonstration with Lila fails because she is able to resist his will. Von Altermann later becomes alarmed after Lila disappears, and Keating also disappears while searching for her. Larry continues to investigate and becomes friendly with Jennifer, who believes that her employer was devoted to his wife. Although the corpse of a man keeps turning up when Jeff is around, it disappears every time Jeff brings someone to see it. Scott, who has dropped the pretense of being Larry, insists that Von Altermann send for the police, but Von Altermann cleverly arranges for the German agent to impersonate the sheriff. Von Altermann then catches Larry with his secret radio equipment and locks Larry in a closet. Larry escapes with Jeff's help, but in the meantime, Von Altermann has poisoned the dinner with a special drug. Before dinner, Beulah takes Larry to see Lila, who says that only Von Altermann's death will free the zombies. After dinner, Larry and Scott fall unconscious, and Von Altermann takes Scott into the laboratory to turn him into a zombie. Because Larry has only feigned unconsciousness, the agent reveals to him that he is actually a U.S. federal agent working undercover. Before operating on Scott, Von Altermann goes to Jennifer and tells her that he is taking her to Germany to be his wife. Jennifer flatly refuses, then finds Larry, who has banded together with the agent, Beulah, Jeff and Rosella. After forcing their way into the lab, they confront Von Altermann, and are astonished when Lila leads a troop of zombies into the laboratory and they converge on Von Altermann. Von Altermann escapes into the swamp, but Lila forces him into a pool of sucking mud, and they go down together. The zombies return to their graves for good, and Keating reappears and revives Scott. While Scott remains at the mansion to take care of business, Jennifer and Larry leave together, and Rosella goes to New York with Jeff.