It's Halloween in Dimmsdale. Ivan, Chester, A.J. and Tootie come over to the Turner house to trick-or-treat. Timmy's parents give them candy and Timmy invites them over for a party, and they tell scary stories. Tootie begins telling her own story titled "Invader Trixie".
In a parody of Invader Zim, Trixie Tang is a female Irkin soldier, who was a reason for the failure of Operation: Impending Doom. The Almighty Tallest give her the task of infiltrating Earth to find it's weaknesses and observe the customs of the doomed planet for the impending alien invasion by ingeniusly disguising herself as a beautiful human girl. Together with her faithful companion, Ver (who's later disguised as a human girl named Veronica), Trixie must face the Earth's perils to undermine the planet's defenses. One of the failing students in Dimmsdale, Timmy Turner, falls in love with Trixie's human form, completely unaware that she's an alien. However, Timmy's other crush and school's laughing stock, Tootie, is very suspicious, and suspects that Trixie and Veronica are aliens. The next day, Tootie gets in a fight with Trixie, in front of the entire class. Eventually, Tootie defeats Trixie by shoving cafeteria food in her mouth, and exposes Trixie's real alien identity to everyone. Timmy then confesses to the school facility and reveals the awful truth: he's an alien too, and his fairy godparents were actually SIR units this entire time. Timmy and Trixie, along with Ver and his trusty SIR units conquer Dimmsdale.
When Tootie finishes her story, everyone liked it, except for Timmy, who accuses Tootie of making up the story out of jealousy towards Trixie Tang, although he did like the twist ending, even if it came completely out of nowhere. A.J. then begins telling his own story about building a car out of spare junk parts that goes haywire, titled "Maximum Turbocharge".