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.

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.

The monstrous Turbo Toilet 2000 is determined to take revenge on George, Harold, and Captain Underpants.

A skateboarding principal offers unusual incentives to his students to motivate them to learn more.

"Friends and pranking partners Miles and Niles face a tough challenge when their favorite goat and nemesis, Principal Barkin, is replaced by his stern, no-nonsense father, Former Principal Barkin, who turns the school into boot camp"--

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.

On the third day of school, a young boy is sent to the principal's office and thinks about all the horrifying rumors he has heard about her.

"Melville Heights is one of the nicest neighborhoods in Bristol, England; home to doctors and lawyers and old-money academics. It's not the sort of place where people are brutally murdered in their own kitchens. But it is the sort of place where everyone has a secret. And everyone is watching you. As the headmaster credited with turning around the local school, Tom Fitzwilliam is beloved by one and all--including Joey Mullen, his new neighbor, who...

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.

When the new vice principal is put in charge of Ella Mentry School for a few days, she tries out some very unusual ideas about how students learn.