Dee Dee and her friends, Lee Lee and Mee Mee, enter Dexter’s lab and wreak havoc. Dexter clones himself to stop them, but the girls too make clones of themselves.
Dexter catches the chicken pox, and Dee Dee tells him a ridiculous tale that if he keeps scratching them, he will turn into an evil chicken. Dexter completely restrains himself so that he will not have to scratch it; unfortunately, he is unable to resist and his nonstop scratching eventually does just that.
Monkey encounters Simion (Maurice LaMarche), an intelligent anthropomorphic chimpanzee who seeks vengeance on humans for turning him into his current state.
Dexter finds the exact opposite of his family, a hyperactive boy who is like Dee Dee and has scientist parents who are like Dexter. Sensing to fit in, he switches places with the boy.
Dee Dee accidentally shuts down Dexter’s lab, and he has to power it back. In the process, Dee Dee attempts to keep Dexter from finding out what she really did.
After a crime prevention talk at school, Dee Dee, Lee Lee, and Mee Mee become crime fighters, but they unintentionally end up being neighborhood criminals.
After staying up late at his lab, Dexter oversleeps, waking up one minute before his school bus arrives. With no time to do his morning chores and homework, he pulls out a secret prototype device, which converts his last 30 seconds into 30 minutes.
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
Dexter thinks that a crazy homeless person balancing electronic devices on his head and muttering gibberish is a genius trying to contact aliens, so he takes him home.
In a fit of rage, Dexter dumps Dee Dee’s favorite teddy bear into the garbage. An upset Dee Dee begins to behave oddly, prompting Dexter to go to the garbage dump and get it back.
The U.S. army invades Dexter’s lab under the mistaken impression that aliens are using it as a base of operations on Earth, and Dexter must convince them that this is actually his lab, and also has to keep this a secret from Dee Dee.
After Dexter’s pencil rolls to the back of the school bus, Dexter goes to retrieve it, but legend says that no one has ever returned from the back of the bus.