Charlie Chan goes to Egypt on behalf of the French Archaeological Society to investigate Professor Arnold's excavation of Ameti's tomb, because the artifacts discovered in the tomb have been found in other museums.  Once there, however, Chan finds out from the professor's daughter Carol, his son Barry, his brother-in-law, Professor Thurston, and Tom Evans, who is Arnold's young assistant and Carol's boyfriend, that Arnold has been missing for a month.

When Carol is overcome by worry over her father, Tom sends for Dr. Anton Racine, who arrives shortly after Carol hallucinates that she is being menaced by Sekhmet, the goddess of vengeance whose statue was guarding Ameti's tomb.  Meanwhile, in the basement laboratory, Chan, Thurston and Tom examine Ameti's mummy using an X ray.  When Chan notices a bullet in the mummy's chest, they unwrap it and discover not Ameti but Professor Arnold.  Thurston then tells Chan that he sold the artifacts to pay off money he had borrowed from Racine.

Barry overhears them discussing his father's death and collapses in hysterics, certain that the tomb's curse will kill the entire family.  Chan decides to investigate the tomb that night, so with Tom and his helper Snowshoes, he sets off, but once inside the tomb, they are frightened off by a vision of Sekhmet.

The next day, Chan goes to Luxor to question Daoud Atrash, the chemist who fills Racine's prescriptions for Carol.  That night, when Chan returns to the Arnold house, an autopsy of the professor is underway, and after the others leave, Chan extracts the bullet from near Arnold's heart.  Chan then rejoins the others upstairs and questions Racine about Mapouchari, a drug which causes hallucinations and death, and which Chan suspects is placed on Carol's cigarettes to trigger her attacks.  They are just about to talk to Barry about the secret treasure his father was trying to find when Barry dies while playing his violin.

Later, Chan, Tom and Snowshoes return to the tomb, where they find a secret water passageway.  Tom swims to the next room, which is a storage room for Ameti's treasures, but he is shot by someone he recognizes.  As he falls, he hits a lever that opens a door between the rooms, and Chan and Snowshoes take him back to the house.  After the bullet is removed, Chan takes it for evidence, then goes to search Barry's room.  Chan deduces that Barry was killed by a tiny vial of the deadly drug.  He demonstrates to Thurston and Racine how the violin's vibrations shattered the glass, releasing the drug in gaseous form.  He then tells them it was the hidden treasure room which was the motive for the two murders and the attempt on Tom's life.

Upstairs, Racine examines Tom, after which Thurston sends Carol to rest.  Alone with Tom, Thurston prepares to stab him in his wounds with Racine's lancet, but Chan arrives just in time.  Chan explains that the bullets recovered from Arnold and Tom came from Thurston's gun, and the police then take Thurston away.  Tom regains consciousness and is enfolded in Carol's loving embrace.