In the 1920s, Tennessee schoolteacher Bertram Cates (Dick York) is put on trial for violating the Butler Act, a state law that prohibits public school teachers from teaching evolution instead of creationism. Drawing intense national attention in the media with writer E. K. Hornbeck (Gene Kelly) reporting, two of the nation's leading lawyers go head to head: Matthew Harrison Brady (Fredric March) for the prosecution, and Henry Drummond (Spencer Tracy) for the defense.