In need of an assistant to operate his latest invention, Dexter performs a brain transplant on Dee Dee to make her smart enough to fulfill the role. With her new brain, Dee Dee proves to be more intelligent than Dexter.
Dexter and Dee Dee listen in on their parents’ conversation; they are playing Scrabble, but the way they talk makes it sound like Dad was cheating on Mom
After watching an Action Hank movie on television, Dexter grows a synthetic beard to try to be cool, but the police mistake him for Action Hank himself.
Dexter’s family goes to the beach, where Dexter tries to communicate with whales. He must rescue Dee Dee (dressed as a mermaid), when she is captured by manic pirates.
Dee Dee dares Dexter into building her a giant robot similar to his Robo-Dexo 2000. They then team up to try to save an island’s population from being destroyed by an erupting volcano using their giant robots.
Dexter’s school and parents decide to send him to college. He ignores his fellow students, who prefer to “party now, study later”, until his mind finally snaps from the workload.
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.
After Dexter orders and eats a giant burrito, he suffers severe stomach pains. Believing a test the computer gave him, he assumes that he has only 30 minutes to live.
Dexter travels to the moon and finds that aliens are planning an invasion on Earth, and he uses his Robo-Dexo 2000 to stop them. It turns out that they only were interested in purchasing sweaters for the winter.
Dexter accidentally gives himself telepathy that he cannot shut off when trying to overhear his father’s thoughts to figure out what he got for his birthday, causing everyone to accidentally read his own mind.
Dexter and Dee Dee’s secret decoder rings hold the keys to joining the Action Hanks and Pony Puff fan clubs respectively, but they interchange the clues by mistake, causing them to switch clubs.
On his birthday, Dexter makes himself invisible so that he can find out whether his parents have bought him the Major Glory action figure he always wanted.