Captain Underpants and the revolting revenge of the radioactive robo-boxers

A world without underpants? when we last saw our heroes, george and harold, they had been turned into evil zombie nerds doomed to roam a devastated, post apocalyptic planet for all eternity. But why, you might ask, didn't the amazing captain underpants save the boys from this frightening fate? because tippy tinkle trousers and his time-traveling hijinks prevented george and harold from creating captain underpants in the first place! now, having changed the course of human history forever, they'll have to figure out a way to change it back. Could this be the end for captain underpants?!!