Captain Underpants and the Terrifying Re-Turn of Tippy Tinkletrousers

Tippy has come from the future, and in the last book George and Harold are arrested for the crimes that their alternate versions did, and the two (and Krupp) are imprisoned. At the Piqua State Penitentiary, Tippy is asked to build a statue (secretly a robot suit) of Warden Gordon, the chief jailer of the prison. On the day Tippy presents his robot suit, he freezes everyone in his way, then takes Krupp to find the boys for Tippy. George and Harold snap their fingers bringing Captain Underpants to life, and soon, while trying to freeze him, Tippy accidentally freezes his robotic legs. Even though Captain Underpants successfully pulls off the top half of the robo-suit, Tippy escapes by going back in time to a bit over five years ago.

Moved in from Michigan, five-and-three-quarters-year-old George's mother makes him wear a tie as a good first impression. On his way to school, he notices six-year-old Harold being attacked by Kipper and his group, with the mean owner of a gas station, Billy Bill, egging them on. Angered at this, George plays a smart prank on the owner by changing his gas station's sign from "Free Brake Inspection" to "Free Bra Inspection", prompting a group of infuriated and offended women to attack the latter (and maybe even strangle him to death!). George then saves Harold and the two become best friends. Mr. Krupp arrives and sends the two to detention for "bullying Kipper". To pass time, the two make their first comic: The Adventures of Dog Man.

George and Harold study Kipper for a week and then later switch his padlock for one of their own locks, and replace his stolen lunch money with girly things like friendship bracelets, dresses, and dolls, while sending strange texts to Kipper's goons, all while placing a note from "Wedgie Magee" with it. However, Kipper eventually catches on to the setup and, the next day, him and his gang steal the pizzas that George and Harold bought for the kindergartners as a way to torture them even further. Infuriated, the two friends come up with another major prank on the bullies in retaliation. First, they fill the four bullies' lockers with shaving cream to pass it off as ectoplasmic ghost juice. While initially this works, Principal Krupp points out that the "ectoplasm" was obviously sprayed through the vents on doors. Enraged and tired of the anonymous pranks, Kipper and his friends begin to torture the kindergarteners for answers, even stealing more pizzas, which George and Harold were actually counting on them to steal, as they ordered them to have double ghost chili peppers (Piqua Pizza Palace's hottest chili peppers) which cause the bullies' tongues to burn up completely, resulting in them getting sent to the nurse's office. George and Harold eventually create a comic that tells the tale of Wedgie Magee and the signs of his curse, all of which match their pranks. After Kipper and his gang "see" that ghost (George on stilts, wearing a giant pair of pants), they run outside in terror, during a severe thunderstorm and power outage. In the original timeline, they then apologize for their deeds, compensate the kindergartners, and never bully anyone again. Unfortunately, Tippy arrives in the past at exactly the same time Kipper's gang runs outside. The four bullies go insane from fear as Tippy's robot closely resembles the ghost of Wedgie Magee.

This causes the police to accuse Principal Krupp of causing Kipper and his friends' insanity despite no charges being filed against him, which eventually results in him permanently losing his job. Tippy then time travels four years back in the future, believing that kids five years ago were weird. However, as Mr. Krupp was hypnotized to become Captain Underpants when George and Harold were in the 4th grade, a paradox happens, and a universe is created where Captain Underpants never existed. Tippy arrives in the present only to find out all that remains of Earth is a flaming and devastated wasteland (caused by Dr. Diaper's Laser-Matic 2000) overrun by talking toilets and giant evil zombie nerds (because the boy whose mother thinks he talks crazy tells Tippy everything). Tippy realises that he has to go back again and save Earth. However, Tippy immediately gets squashed by George and Harold, who are now giant zombies nerds. What remains left of Tippy is a red squishy stain, appearing to be blood.

• George Beard – A ten and three-quarters year old boy.
• Harold Hutchins – An eleven-year-old boy.
• Mr. Krupp - The principal of George and Harold.
• Captain Underpants – Mr. Krupp's alter-ego.
• Tippy Tinkletrousers – Formerly called Professor Poopypants in the fourth book, but changed his name.
• The Chief of Police – The leader of the cops.
• Officer McWiggly – Right-hand man of the chief.
• Warden Gordon Bordon Schmorden – The chief jailer of Piqua State Penitentiary.

• George Beard – A five-and-three-quarters year old boy.
• Harold Hutchins – A six-year-old boy.
• Mr. Krupp – The principal of George and Harold, and uncle of Kipper.
• Kipper Krupp – The captain of the sixth-grade wrestling team, school bully of the kindergartners, and nephew of Mr. Krupp.
• Finkstein – One of Kipper's friends and wrestling teammates.
• Bugg – One of Kipper's friends and wrestling teammates.
• Loogie – One of Kipper's friends and wrestling teammates.
• Ladies – An angry mob of offended young, middle-aged, and elderly women who beat up Billy Bill as the result of a prank out of karma, courtesy of George. Two of them resemble Ms. Ribble and Miss Anthrope.
• Billy Bill – The less-than-friendly gas station owner who resembles Mr. Meaner.
• The cheerleaders – Wendy Swan and her girls are the cheerleaders. They became frightened and ran away screaming after they saw a gooey substance that they thought was ectoplasm (but was actually shaving cream).
• Wedgie Magee – A kindergartner in the comic book.
• The gossip girls – 4 gossipy girls who are listened by George.
• The delivery guy – Delivery guy of the Piqua Pizza Palace.
• Ms. Ribble – The teacher of Jerome Horwitz Elementary School.
• Mr. Fyde – The former science teacher of Jerome Horwitz Elementary School and current resident (mentioned in the newspaper) of the Piqua Valley Home of the Reality Challenged.
• Donny Shoemyer – A kindergartner of Jerome Horwitz Elementary School and the first to suffer from Kipper's wrath upon him catching on to the ectoplasm (shaving cream) prank.

Reception for the book was mostly positive,[3][4] with Kidsreads.com praising the entry.[5] Booklist gave a positive review, writing that it would have a definite appeal to kids.[6] Kirkus Reviews gave an ambivalent review, stating that the book's jokes were typical but that there were signs that the "creative wells are running dry at last".[7]

• Crackers and Sulu are notably absent when George, Harold, and Mr. Krupp got arrested.

• Captain Underpants and the Preposterous Plight of the Purple Potty People
• Captain Underpants and the Revolting Revenge of the Radioactive Robo-Boxers

• Captain Underpants and the Terrifying Re-Turn of Tippy Tinkletrousers at Scholastic.com