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.
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. By flipping the pages, the reader may view animated illustrations.
Having changed the course of human history after unwittingly wondering what could be worse than going to prison, George and Harold are catapulted through time back to their kindergarten days, where they are subjected to a sixth-grade bully and a cluelessschool principal.