Captain Underpants and The Terrifying Re-Turn of Tippy Tinkletrousers (Hardcover) Captain Underpants and the Revolting Revenge of the Radioactive Robo-Boxers (hardcover) Captain Underpants and the Tyrannical Retaliation of the Turbo Toilet 2000 (Hardcover) Captain Underpants and the Attack of the Talking Toilets (paperback) The Captain Underpants Extra-Crunchy Book o’ Fun ( paperback) Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy Part 2: the Revenge of the Ridiculous Robo- Booglers (Paperback) The series revolves around two fourth graders, George Beard and Harold Hutchins, living in Piqua, Ohio, and Captain Underpants, an aptly named superhero from one of the boys' homemade comic books, who accidentally becomes real when George and Harold hypnotize their cruel, bossy, and ill-tempered principal, Mr. Krupp.