An ancient Egyptian priest called Imhotep is revived when an archaeological expedition in 1921, led by Sir Joseph Whemple, finds Imhotep's mummy. Imhotep had been mummified alive for attempting to resurrect his forbidden lover, the princess Ankh-es-en-amon. Whemple's friend, Dr. Muller inspects the mummy and exclaims "The viscera were not removed. The usual scar made by the embalmers knife is not there." Sir Joseph Wimple responds, "I guessed as much." Muller then deduces that Imhotep was buried alive for sacrilege. Despite Muller's warning, Sir Joseph's assistant Ralph Norton reads aloud an ancient lifegiving scroll – the Scroll of Thoth. Imhotep escapes from the archaeologists, taking the Scroll of Thoth, and prowls Cairo seeking the modern reincarnation of Ankh-es-enamon.
10 years later, Imhotep is masquerading as a modern Egyptian named Ardath Bey. He calls upon Sir Joseph's son, Frank and Prof. Pearson. He shows them where to dig to find Ankh-es-en-amon's tomb. The archaeologists find the tomb, give the mummy and the treasures to the Cairo Museum, and thank Ardath Bey for the information.Imhotep encounters Helen Grosvenor, a woman bearing a striking resemblance to the Princess. Believing her to be Ankh-es-en-amon's reincarnation, he attempts to kill her, with the intention of mummifying her, resurrecting her, and making her his bride. She is saved when she remembers her past life and prays to the goddess Isis to save her. The statue of Isis raises its arm and emits a beam of light that sets the Scroll of Thoth on fire. This breaks the spell that had given Imhotep his immortality, causing him to age rapidly and then crumble to dust. At the urging of Dr. Muller, Frank calls Helen back to the world of the living while the Scroll of Thoth continues to burn.