The story revolves around an effort by the Southern Engineering Company to drain a swamp for public benefits, but their mission is quickly hampered by the local workers' superstitions. Many believe the area is haunted by the mummy Kharis and his bride, an ancient legend dating back 25 years. As the workers' fears grow, two representatives from the Scripps Museum, Dr. James Halsey and Dr. Ilzor Zandaab, arrive on-site to investigate the disappearance of ancient mummies buried in the swamp. They introduce themselves to Pat Walsh, the project head, and reveal their goal of uncovering the missing mummies, but their presence is soon overshadowed by ominous events.
Not long after their arrival, a worker is mysteriously murdered in the swamp, leading Dr. Halsey to suspect that the killer has found Kharis’s mummy, triggering a series of disturbing discoveries. During the night, Zandaab sneaks into the swamp for a clandestine meeting with Ragheb, a disciple of the Arkam sect, where it is revealed that Zandaab is secretly a High Priest. The scene intensifies as Zandaab brews a potion from tana leaves and explains the legend of Kharis and Princess Ananka, who is depicted as a victim of an ancient curse.
Their ritual is disrupted when the old sacristan of the monastery, who intrudes on their sinister proceedings, is quickly killed by a resurrected Kharis. Meanwhile, during an excavation, the tomb of Ananka is partially uncovered, causing her mummy to rise from the swamp. She immerses herself in a pond, which washes away her wrappings and reveals her youthful, beautiful face — a stark contrast to her previously mummified form.
The young woman, calling out the name "Kharis," is soon discovered wandering the swamp by Cajun Joe, who takes her to Tante Berthe, the owner of the local tavern. She is cared for there, but Kharis soon finds her and murders Tante Berthe in his silent, relentless way. Ananka, still unwell but alive, flees into the night and is later found unconscious beside the road by Dr. Halsey and Betty Walsh, Kay Harding’s character. Though she appears to suffer from amnesia, the girl displays an uncanny knowledge of ancient Egypt, hinting that her mind is still connected to her past.
As they try to help her recover, Kharis appears again, attacking Cajun Joe in his quest to find her. Ananka seeks refuge in Betty’s tent, but Kharis follows and abducts her, leaving Betty terrified and helpless. Betty then seeks Ragheb’s assistance, but he betrays her, taking her to the monastery instead. Meanwhile, Zandaab, furious that Ragheb is making advances on Betty after already having administered the tana fluid to Ananka, orders her death, but Ragheb intervenes and kills Zandaab instead.
The climax unfolds as Dr. Halsey arrives just in time to face Ragheb at the monastery. A fierce struggle ensues between Ragheb and Halsey, which is interrupted by Kharis, who, sensing Ragheb's treachery, turns on him and crushes him beneath the monastery walls. The story concludes with Halsey, Betty, and the others discovering the mummified remains of Ananka, ending their horrifying encounter with the ancient curse and the eerie presence of Kharis.
