 A take on the classic tale  The Boy Who Cried Wolf ,  Big Fat Liar  is about a 14-year-old boy named Jason Shephard (Frankie Muniz) who lies for the fun of it. Jason loses an important story assignment entitled  Big Fat Liar  in movie producer Marty Wolf s (Paul Giamatti) limo, which Wolf then turns into a film. When Jason sees a movie preview of his story, he and best friend Kaylee (Amanda Bynes) go to Los Angeles to make Wolf confess to using Jason s story as well as to clear Jason s name and to get him out of having to attend summer school. The teen liar then has to match wits with Wolf, who also turns out to be a big liar.