Phillip Browning, Frank M. Thomas, is convinced that the ten deaths among his colleagues stem from a mummy's curse, and he hopes to avert the same fate by returning King Pharatime's treasures to their tomb. Ditch diggers Stanley Wright, Bert Wheeler, and Aloysius C. Whittaker, Robert Woolsey, answer a newspaper advertisement to join Browning's Egyptian expedition. Whittaker pretends to be an Egyptian expert, and Wright—who is immediately attracted to Browning's daughter Mary Browning, Barbara Pepper—struggles with spells of forgetfulness that can be cured only by taking a nap, a running gag that threads through the voyage. Browning hires them anyway.
On board the ship to Egypt, Dr. Edward Sterling, Moroni Olsen, joins the expedition as a member. Catfish, Willie Best, a stowaway, is invited to join after he mentions he is from Cairo—though Whittaker and Wright later discover he is from Cairo, Illinois. After they reach their hotel, Sterling disappears and a threatening note is found.
Soon after, Whittaker, Wright and Mary Browning awaken to find Catfish tied up and everyone else gone. They discover another threatening note in Browning's tent and are directed to dig to the tomb entrance and move the boxes containing the treasures inside. They work until the entrance is clear and begin transferring the boxes, while the scene cuts to a secret tomb chamber where Sterling has Browning tied and gagged. Sterling reveals that he murdered the other ten with a syringe of undetectable poison and plans to do the same to Browning, Mary, Whittaker and Wright. He leaves, but drops a diary, which Wright later recovers.
A landslide seals the tomb entrance, trapping Whittaker, Wright, Mary and Catfish inside. Sterling reappears, posing as a kidnapping victim and professing belief in the curse. Wright reveals that he has read the diary but cannot recall where he hid it. Sterling offers to inject him with a sedative, but Wright, fearing the syringe, leads a chase that ends when he knocks Sterling over the head with a vase. The vase shatters, revealing the diary, which Whittaker picks up and uses to identify Sterling as the killer.
The police arrive at the camp, enter the tomb, and arrest Sterling. Rasheed Bey, the Egyptian spy who had warned Wright over the phone, Francis McDonald turns out to be an undercover investigator tracking Sterling.
In the fadeout, Wright has something he wants to say to Mary Browning, Barbara Pepper, but he cannot remember what it is.
