George and Harold and their doubles, Yesterday George and Yesterday Harold, have been taking turns going to school, but when the doubles fall prey to their gym teacher, Mr. Meaner, and his method of mind control that turns students into attentive, obedient, perfect children, it is up to original George and Harold to strike back.

Harold and George's time-traveling Purple Potty lands them in an alternate universe where everything seems delightful, but evil lurks just beneath the surface, and leads to a battle between Captain Underpants and his own evil twin.

After his time-traveling deeds cause the destruction of the world by preventing Harold and George from creating Captain Underpants, Tippy Tinkletrousers tries to use his time machine to correct the situation, but it proves to be difficult to fix -- Publisher.

When Professor Pippy P. Poopypants comes to Jerome Horwitz Elementary School to teach science, and he goes off the deep end because students make fun of his name, only Captain Underpants can save the school from the professor's perilous plot.

George, Harold, Captain Underpants, and Sulu the bionic hamster battle the three ridiculous Robo-Boogers in an attempt to turn the Bionic Booger Boy back into Melvin Sneedly.

Principal Krupp once again turns into the superhero Captain Underpants in order to save the world, and Jerome Horwitz Elementary School, from the evil talking toilets and the Turbo Toilet 2000.

Only Captain Underpants can stop the three evil space aliens who have invaded Jerome Horwitz Elementary School and turned everyone into lunchroom zombie nerds.

When George and Harold hypnotize their principal into thinking that he is the superhero Captain Underpants, he leads them to the lair of the nefarious Dr. Diaper, where they must defeat his evil robot henchmen.

George and Harold are fourth-grade buddies with a penchant for practical jokes. When the boys' latest prank drives their science teacher over the edge, their clueless principal, Mr. Krupp, quickly hires a replacement: Professor Pippy P. Poopypants. Of course, George and Harold can't resist making fun of the Professor's silly name. But then the Professor retaliates by forcing everyone in town to change their own names to be equally silly, with colossal...

A snotty situation ensues when Melvin Sneedley, an academically-gifted student, turns into the Bionic Booger Boy and must be stopped by George, Harold, and Captain Underpants.