After struggling to establish himself, author Emile Zola (Paul Muni) wins success writing about the unsavory side of Paris and settles into a comfortable upper-class life. However, Zola's complacency is shaken when Jewish officer Alfred Dreyfus (Joseph Schildkraut) is imprisoned for being a spy. Realizing that Dreyfus is an innocent victim of anti-Semitism, Zola boldly pens a newspaper article exposing the truth, is charged with libel and must defend himself in a dramatic courtroom testimony.