Mandark Astronomanov, a new student at Dexter’s school, seems to be superior to Dexter academically. Mandark forces Dexter to shut down his lab so that Mandark’s lab can gain more power. However, with the help of Dee Dee, Dexter manages to destroy Mandark’s lab.
While out for dinner at a pizza restaurant, Dexter tries to slow down the “Whack the Weasel” machine to win a stuffed Monkey doll before Dee Dee does. Security captures him for tampering with the machine, and he falls into the hands of a mad scientist.
Suspicious that Dee Dee has not entered his lab even once on a particular day, Dexter shrinks himself and enters her room to spy on her. He soon becomes an unwilling character in Dee Dee’s doll story, but he believes the story to be real.
Not interested in hearing Dee Dee’s long-winded story, Dexter gives her a silencing formula to keep her quiet, but it instead turns her into a giant monster still bent on telling her story. When he realizes that nothing can make her quiet, he becomes a giant monster himself.
Dexter’s father is challenged to an arm wrestling match by a man named Earl at a truck stop. Stunned at the strength of Earl and his determination to beat his father, Dexter attaches a robotic arm to his father to enable him to win.
After being denied dessert by his parents for not eating his vegetables, Dexter uses radiation therapy so that he can like vegetables, but it causes a severe side effect that turns him into an Incredible Hulk-like character if he goes too long without them.
Mandark brings his lab duck Ducky for show and tell to counter Dexter and his lab monkey. Though neither creature displays remarkable characteristics at school, Ducky, unbeknownst to Mandark, is the alter ego of supervillain Quackor the Fowl.