Captain Underpants and the Revolting Revenge of the Radioactive Robo Boxers

Plot

The book picks up right where the previous one left off. Through misdirection, it is revealed that Tippy was not killed at the end of the last book, but instead giant zombie nerd Harold crushed a giant ketchup packet (the book reveals that giant things such as the zombie nerds move really slowly). Tippy Tinkletrousers arrives on an Earth without Captain Underpants. He then vows to change everything back to normal and travels back to the night when Kipper and his friends encounter him (though he travels to 5 minutes earlier to position himself behind the school). They are frozen before they see him, thus they do not go insane, and Mr. Krupp is not fired. Tippy shrinks and abducts his past self, and time travels away right before Kipper and his friends are unfrozen.

He then travels forward in time four years to when George and Harold were about to be arrested (the end of the eighth book). The boys then decide to send their pet pterodactyl Crackers back to the dinosaur age with Sulu, their hamster. The boys then travel back in time, but accidentally take Mr Krupp with them. Eventually, a second Tiny Tippy, slightly younger than the original one, was created to find out where George and Harold went.

Tippy and his two miniature clones then travel back to the dinosaur age (65 Mya) and pursue the boys and Captain Underpants. The tiny Tippies zap themselves back in time and steal the Goosy-Grow 4000, which transforms Tiny Tippy into the colossal Supa Mega Tippy, who betrays Slightly Younger Tiny Tippy. When Big Tippy attempts to use his nuclear bomb to kill Captain Underpants, Supa Mega Tippy zaps himself back in time (with his twin) after kicking Big Tippy and his bomb away into the Gulf of Mexico. When the bomb explodes, it blows a huge crater and kills the dinosaurs (a parody of the Cretaceous–Paleogene extinction event).

The five protagonists and their captor then travel to the African savannas where the boys and their pets gain the trust of some cavemen who inhabit the surrounding jungles. The cavemen are taught English through drawings and subsequently, the boys make the world's first comic book (which involves drawing of traps working on Tippy). The Neanderthals, inspired by the book, then set traps for Tippy and defeat him. He then sets off his freeze ray (which has been tampered with by his younger twin so that it could not be turned off), and the Goosy-Grow enlarges the ice which appears to make Crackers' condition deteriorate and causes the Ice Age (and freezing Tippy himself).

George and Harold are then transported to the future by Slightly Younger Tiny Tippy where it turns out they are now teachers (the mean and cruel ones they are used to) and Mr Krupp is an old man. After getting rid of their evil future selves, old Mr. Krupp gets hypnotized into Captain Underpants, and through the boys' willpower, Captain Underpants and his older counterpart beat up Tippy, who afterwards attempts to use his nuclear bomb to blow up the galaxy. After that, Crackers and Sulu decide to save the entire galaxy by sending Tippy and themselves back to the time before the universe existed. The three are then destroyed by Tippy's giant nuclear bomb and the universe is formed. It also turns out that Crackers had laid a brood of eggs (revealing Crackers to have been a female.) and George, Harold and Captain Underpants decide to take care of them. Suddenly Melvin Sneedly, in a giant squid called the "Supa Squid", appears and captures George, Harold, and Captain Underpants, taking them back to the present.

Characters

Trivia