George and Harold won't be able to participate in this year's science fair. That's because they glued Principal Krupp to his chair at last year's science fair. But that won't stop them from messing with the science projects. So the electric dog washer shoots out black ink, the model volcano blows out butterscotch pudding, and the boys end up in detention. With time to kill, they create a new Captain Underpants episode, this one with attacking toilets. But when the school science genius turns the cartoon into reality, it's time for Mr. Krupp to transform into everyone's favorite underwear-wearing superhero!