Captain Underpants and the Preposterous Plight of the Purple Potty People

Captain Underpants and the Preposterous Plight of the Purple Potty People is the eighth book in the Captain Underpants series by Dav Pilkey.

Plot Continuing from the last book, George, Harold, Sulu and Crackers end up in an alternate universe where the whole world is the opposite of their normal world. Good is bad, smart is not at all intelligent, and heroes are villains. For example, Melvin Sneedly is struggling to comprehend a simple children's book and Mr. Krupp is nice and has a sense of humor. There they meet Captain Underpants's evil twin, Captain Blunderpants (Mr. Krupp's super-villain identity) and evil versions George and Harold (George and Harold's evil counterparts) Sulu and Crackers are kidnapped by George and Harold's evil counterparts and are hypnotized to be evil. Sulu becomes evil and attacks the good George and Harold but Crackers on the other hand, saves them (Briefly because Crackers might be a female and hypnosis does the opposite on females)

The heroes finally get back to the normal dimension of the world, but end up bringing the Mr. Krupp of the alternate universe, Sulu, and the evil George and Harold with them. The evil George and Harold transform their Mr. Krupp into Captain Blunderpants by getting water on his head. It is Grandparents Day and George and Harold have to eat dinner with their grandparents at George's house. While there, the evil George and Harold find George and Harold's house, rummage through their personal belongings and find the "Goosy-Grow 4000" and transform Sulu into a giant monster. George and Harold fly over on Crackers' back, and decide that they have to drink the super power juice, but unfortunately, it is empty. They find Captain Underpants who defeats the "Giant-Evil Sulu". Captain Blunderpants is transformed back into the nice Mr. Krupp by the snap of the finger, and Captain Underpants ties them up, but when Harold states that nothing can go wrong, the worst thing is that something can go wrong, this causes a rain storm to turn the nice Mr. Krupp back into Captain Blunderpants and Captain Underpants is turned back into the mean Mr. Krupp and goes home.

Great Granny Girdle and Boxer Boy (George's great-grandmother and Harold's grandfather) are made super-heroes when they drink the super power juice and they defeat Captain Blunderpants. Sulu is shrunk and turned good again and Captain Blunderpants and the Evil George and Harold (now shrunken) are taken back to their world.

Harold once again states that nothing can go wrong, but this causes police men to arrest them because they think they are the evil George and Harold, who robbed a bank while Captain Underpants was fighting Sulu. Harold again states that things cannot get any worse because they are going to jail for the rest of their lives. This time, however, Tippy Tinkletrousers (Professor Poopypants who changed his name at the end of the fourth book) comes and chases George and Harold. The book ends, once again, with George yelling "Oh no!" and Harold yelling "Here we go again!"