In the city of Piqua, Ohio, two fourth-grade friends and next-door neighbors named George Beard (Kevin Hart) and Harold Hutchins (Thomas Middleditch) are the pranksters at their school, Jerome Horwitz Elementary School. They excessively pull numerous pranks on the cruel teachers, many of which are directed at their mean-spirited principal, Benjamin Krupp (Ed Helms), putting the two at odds with him. The duo also create comic books about a superhero named Captain Underpants, who fights crime while wearing underwear and a cape. They distribute these to their schoolmates through a comic company called Treehouse Comix Inc., located in their tree-house. George and Harold's pranks come to an apparent end after they're caught tampering with a toilet invention, the Turbo Toilet 2000, made by the school's local snitch and intellectual, Melvin Sneedly (Jordan Peele), on video with Melvin's tattle-turtle. Finally having solid proof of the boys' antics, Mr. Krupp excitedly prepares to annihilate their friendship by putting them in separate classes..