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 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.

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.

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

Regency England amid music lessons and garden parties, whispered confessions and secret yearnings, one of the school's teachers, headmistress Claudia Martin will find her well-ordered world jolted by love when she meets a man who would make the perfect husband ... for somebody else.

George and Harold hypnotize their principal who, believing he is the superhero Captain Underpants, leads them to the lair of the nefarious Dr. Diaper. They must then defeat his evil robot henchmen.