Having crashed into the Egyptian desert Scrooge, the children, and Launchpad enter the Lost Pyramid of Toth-Ra, only to find it inhabited by "living mummies": descendants of Toth-Ra's original followers who wear mummy-like wrappings and who have spent their entire lives in the depths of the pyramid. To Scrooge's horror, Webby and Louie become separated from them and end up in the Pharaoh's Chamber, which the mummies refuse to enter out of fear of their god-king. Finding himself in a room full of treasure, Louie quickly desires to claim it, but is warned against it by Webby despite her inability to translate all the writings on the wall of the tomb. Meanwhile, the rest of the party learns that the mummies serve Toth-Ra in exchange for paltry exposure to sunlight, and attempt to rally them to rebellion, only succeeding when Launchpad offers them a new wonder: burritos.
Webby and Louie are discovered by a guard who traps them and is about to throw them into a spiked pit, but they are able to escape due to a combination of Louie's smooth-talking and Webby's bizarre fixation on being "sacrificed properly." Webby gets on Louie's case for always seeking to manipulate situations to his own benefit, but he ends up inadvertently alerting her to the location of a secret passage. Meanwhile, Scrooge is dismayed by the "rebellion" he is attempting to lead: Dewey is forming several of the mummies into a dance team, another keeps shutting down Huey's strategies by citing Toth-Ra's supposed omnipotence, and Launchpad is training the rest to make burritos. Louie and Webby return to the treasure chamber and are confronted by Toth-Ra, only to learn that he is a lifeless mummy. They then discover that the guard who captured them before is the latest in a long line of charlatans who have used Toth-Ra's body to perpetuate their own hold on the mummies.
The mummies soon break into the treasure chamber, but Toth-Ra's body is inadvertently pulled across a seal in the floor that-as Scrooge is able to decipher-it was never meant to cross. The seal unleashes magic that reanimates Toth-Ra, who begins attacking the mummies, Scrooge, the children, and Launchpad. However, the rebels have now gained a desire for true freedom-beyond just burritos-and help to battle him, with Louie eventually admitting his manipulative nature. Together, the unlikely allies are able to return Toth-Ra to his chamber and his lifeless state before making their way out of the pyramid. They then celebrate by taking all the mummies to a food truck, during which Louie apologizes to Webby and thanks her while Scrooge discovers his own enjoyment of burritos.