Dexter travels to Mars to find intelligent life, unaware that Dee Dee has stowed away in his space capsule. After Dee Dee gets covered in red dirt, Dexter thinks she is a real-life Martian.
When Dexter’s friends become tired of his complicated traps and cheating while playing a role-playing game, they put Dee Dee in his place. She changes the style of play, which annoys Dexter but impresses his friends.
Mandark gets inside Dexter’s computer system and creates a computer virus, so Dexter must follow him inside and kick him out from cyberspace. However, Dee Dee has other plans in mind.
When Dexter is asked to bring his mother to school, he disguises Dee Dee as her so that she can take her place, but Dee Dee does not behave like their mother.
Dexter and Dee Dee enter tryouts to become Major Glory’s sidekick. When Dee Dee wins, Dexter realizes that fancy costumes are not the only criterion to become a superhero.
Dexter falls victim to one of his own inventions and sends Dee Dee back in time to warn his past self about the consequences, but the past Dexter proves hard to convince.
Dexter’s father sleepwalks into Dexter’s lab. Dexter discovers this, and now has to escort him out of the lab without waking him up, which proves more difficult than thought.
Dexter’s lab is threatened with repossession unless he can repay his debt to NASA. When Dee Dee wins the same amount in a lottery, he decides to steal her money out of desperation.
Banned from watching a late-night movie due to his young age, Dexter uses his technology to artificially grow into adulthood, but Dee Dee tampers with his machine, causing Dexter to turn into an old man.
Dexter has a crush on his teenage babysitter Lisa (Kath Soucie). When he finds out that she has a boyfriend, he sabotages their relationship and accelerates his age by ten years in an attempt to win her heart.
When his television show is interrupted by the Emergency Broadcast System, Dexter sets about fixing any emergencies in the neighborhood to make the signal go away.
