"George and Harold are behind bars for a crime they didn't commit! But just as they are settling into their new life, they are pulled from prison by a time-traveling tyrant named Tippy Tinkletrousers! Now the boys are taking a trip back in time to the carefree days of kindergarten, when the scariest thing they had to face was not evil mad scientists or alien cafeteria ladies but a sixth-grade bully named Kipper Krupp, the nephew of their clueless school principal. And because George and Harold don't invent Captain Underpants until they're in fourth grade, the clever kindergartners are on their own. Can they beat the bullies with brainpower instead of Wedgie Power?"--

After being sent to jail for the rest of their lives, George and Harold are taken on a trip back in time by Tippy Tinkletrousers back to their Kindergarten days where they must deal with their bully without the help of Captain Underpants.

Having changed the course of human history after unwittingly wondering what could be worse than going to prison, George and Harold are shot through time back to kindergarten, where they are subjected to bullying and a clueless school principal.