After an all night sci-fi movie marathon, Candace is convinced that Ferb is an alien and she gathers evidence to prove it. The boys admit to doing something alien-esque, and Candace becomes increasingly frustrated when her plan to bust her brothers is compromised by the alien disguised as someone else in the family. Meanwhile, Dr. Doofenshmirtz is trying to sell an evil "-inator," ostensibly as a cleaning device.
Phineas and Ferb decide to trick out the kiddie rides in front of the Tri-State Mart. Determined to bust them, Candace sits in a rocket ride so it can't go anywhere until Mom shows up, but the rocket launches and Candace flies across Danville. Meanwhile, Dr. Doofenshmirtz plans to leave behind a legacy by burning his name into the atmosphere using his ozone "deplete-inator."