An eighth grader named Jason (Frankie Muniz from ‘Malcom In The Middle’) presents elaborate excuses for never completing his class assignments. Finally his teacher catches him in one of his worst lies ever, and she threatens him with summer school if he doesn’t get his assignment to her by that evening. With all that experience as a creative fibber, Jason writes a brilliant story entitled ‘Big Fat Liar’. With five minutes to spare, Jason races to get it to his teacher when a limousine crashes into him. The occupant, a sneaky Hollywood producer named Marty Wolf (Paul Giamatti) gives Jason a ride, and Jason accidentally drops his assignment in the limo. Jason has to go to summer school and it sucks. But when he sees a preview for the movie that Marty made from the his story, he decides to exact revenge on the producer. He enlists Kaylee (Amanda Bynes), his best friend, to help him on his mission. They travel to Los Angeles and concoct a series of silly schemes to foil Marty’s plans for fame and fortune with Jason’s stolen story.