Captain Underpants and the Sensational Saga of Sir Stinks-a-Lot (Used Book) - Dav Pilkey
George and Harold, and their doubles, Yesterday George and Yesterday Harold, have a good thing going. Two of them go to school, while the other two hide in the tree house and play video games all day -- then they switch! But it turns out there's something rotten in the state of Ohio, and it's smellier than a pile of putrid gym socks. The boys' malicious gym teacher, Mr. Meaner, has created a method of mind control that transforms their fellow students into attentive, obedient, perfect children. Now the future of all humanity is in George and Harold and Yesterday George and Yesterday Harold's hands!
Captain Underpants # 12