George and Harold have been turned into evil zombie nerds doomed to roam a devastated, postapocalyptic planet for all eternity! Unfortunately, the boys can't count on Captain Underpants for help because Tippy Tinkletrousers and his time-traveling 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 out a way to change it back!