Captain Underpants and the preposterous plight of the purple potty people. Dav Pilkey. 2006.

Have George and Harold completely lost their minds? Their time-traveling Purple Potty has landed them in a crazy place where the teachers are always nice, the cafeteria serves delicious food, and the school principal Mr Krupp, actually thinks they’re funny. Something is very, very wrong - and it gets even wronger when the boys’ pet pterodactyl, Crackers, and Sulu the Bionic Hamster are kidnapped by George and Harold’s evil-twin look- alikes. Now George and Harold must face their cleverest enemies yet: THEMSELVES! Could this be another job for the amazing Captain Underpants?