In Egypt in 1895, archaeologists John Banning (Cushing), his father Stephen (Felix Aylmer) and his uncle Joseph Whemple (Raymond Huntley) are searching for the tomb of Princess Ananka, the high priestess of the god Karnak. John has a broken leg and cannot accompany his father and uncle when they open the tomb (According to Cushing's diary, he had twisted his leg before the filming, so the script was adapted to let him recover.) Before they enter, an Egyptian named Mehemet Bey (George Pastell) warns them not to go in, lest they face the fatal curse against desecrators. Stephen and Joseph ignore him, and discover within the sarcophagus of Ananka. After Joseph leaves to tell John the good news, Stephen finds the Scroll of Life and reads from it. He then screams off-screen and is found in a catatonic state.Three years later, back in England, Stephen Banning comes out of his catatonia at the Engerfield Nursing Home for the Mentally Disordered, and sends for his son. He tells him that when he read from the Scroll of Life, he unintentionally brought back to life Kharis (Lee), the mummified high priest of Karnak. He was sentenced to be entombed alive to serve as the guardian of Princess Ananka's tomb as punishment for attempting to bring her back to life out of forbidden love. Now, Stephen tells his disbelieving son that Kharis will hunt down and kill all those who desecrated Ananka's tomb.Meanwhile, Mehemet Bey, revealed as a devoted worshiper of Karnak, comes to Engerfield under the alias of Mehemet Akir to wreak vengeance on the Bannings. He hires a pair of drunken carters, Pat and Mike, to bring the slumbering Kharis in a crate to his rented home, but the two men's drunken driving cause Kharis' crate to fall off and sink into a bog. Later, using the Scroll of Life, Mehemet exhorts Kharis to rise from the mud, then sends him to murder Stephen Banning. When Kharis kills Joseph Whemple the next night, he does so before the eyes of John Banning, who shoots him with a revolver at close range, but to no effect.Police Inspector Mulrooney is assigned to solve the murders but, because he is skeptical and deals only in "cold, hard facts", he does not believe John's incredible story about a killer mummy, even when John tells him that he is likely to be Kharis' third victim. While Mulrooney investigates, John notices that his wife Isobel bears an uncanny resemblance to Princess Ananka. Gathering testimonial evidence from other individuals in the community, Mulrooney slowly begins to wonder if the mummy is real.Mehemet Bey sends the mummy to the Bannings' home to slay his final victim. However, when Isobel rushes to her husband's aid, Kharis sees her, releases John, and leaves. Mehemet Bey mistakenly believes that Kharis has completed his task, and prepares to return to Egypt. John, suspecting Mehemet Bay of being the one controlling the mummy, pays him a visit, much to his surprise.After John leaves, Mehemet Bey leads Kharis in a second attempt on John's life. The mummy knocks Mulrooney unconscious, while Mehemet Bey deals with another policeman guarding the house. Kharis finds John in his study and starts to choke him. Alerted by John's shouts, Isobel runs to the house without Mulrooney; at first, the mummy does not recognise her, but John tells her to loose her hair and the mummy releases John. When Mehemet orders Kharis to kill Isobel, he refuses; Mehemet tries to murder Isobel himself, but is himself killed by Kharis instead. The mummy carries the unconscious Isobel into the swamp, followed by John, Mulrooney and other policemen. John yells to Isobel; when she regains consciousness, she tells Kharis to put her down. The mummy reluctantly obeys. When Isobel has moved away from him, the policemen open fire, causing Kharis to sink into a quagmire, taking the Scroll of Life with him.
Output: Question: Why had Imhotep been mummified alive?, Answer: for attempting to resurrect his forbidden lover, the princess Ankh-es-en-amon