Time Travel Tribulations! George ad Harold have been turned into evil zombie nerds doomed to roan a devastated, postapocalyptic planet for all eternity! 
Unfortunately, the boys can't count on Captain underpants for help because Tippy Tinkletrousers and his time-travelling hijinks prevented George and Harold from creating him in the first place! With Tippy having changed the course of human history forever, George and Harold will have to figure a way to change it back!