The famous French novelist helps free a Jew wrongly convicted by French generals in the infamous Dreyfus case.
In 1862 writer Emile Zola (Paul Muni) and painter Paul Cezanne (Vladimir Sokoloff) try to keep warm in a Paris attic by burning a book. Alexandrine (Gloria Holden) tells Zola she found a job for him as a clerk. Zola is officially warned about his book and loses his job. He sees the homeless, war, and military graft. Zola and Cezanne help a prostitute Nana (Erin O'Brien-Moore), who gives Zola her diary. His novel Nana sells 36,000 in three days. The French army is defeated by Germany, and Zola's book explains why. Generals complain to the censor; but Zola writes more books. Zola has become wealthy, and Cezanne says good-bye.
Major Esterhazy (Robert Barrat) sends a letter to a German general that is stolen and given to the French general staff. The Jewish Dreyfus (Joseph Schildkraut) is suspected. Major Dort (Louis Calhern) has Dreyfus write and arrests him for treason. Dort has his house searched. Dreyfus is found guilty and degraded; but he proclaims he is innocent. Dreyfus's wife Lucie (Gale Sondergaard) visits him in jail, and in 1895 Dreyfus is sent to Devil's Island prison. Col. Picquart (Henry O'Neill) tells the generals that Dreyfus is innocent; but the chief of staff (Harry Davenport) orders Picquart to keep silent. Esterhazy is acquitted.
Lucie Dreyfus calls on Zola and says she has proof and that Picquart is in prison. Zola writes an open letter to the President that the general staff knows Dreyfus is innocent. Zola accuses them in the newspaper and expects a trial for libel. People burn books by Zola, who has to flee a mob. In Zola's trial the judge refuses to re-open the Dreyfus and Esterhazy cases. Zola's attorney Maitre Labori (Donald Crisp) questions Picquart, who explains his proof of Esterhazy's guilt. Lucie is called but not allowed to testify. When Esterhazy is called, the judge orders the court cleared. Esterhazy refuses to answer questions. Major Henry testifies he has proof that Dreyfus is guilty, but he refuses to produce it. The chief of staff confirms it; but Picquart declares the letter a forgery. Zola speaks to the jury for the truth to save the nation's honor. Zola is convicted and is sentenced to one year. Anatole France (Morris Carnovsky) and Georges Clemenceau (Grant Mitchell) advise Zola to flee to London, where he writes articles.
The forger is questioned by the new war minister, admits he forged the letter, and kills himself. Generals resign. Zola is told, and Dreyfus is sent back to France. Zola goes home and writes a book about justice. Zola tells Alexandrine the world must be conquered but not by force of arms. Smoke leaking from a pipe causes Zola's death, and Dreyfus is reinstated in the army. In the final scene Anatole France praises the humanity of Zola and his quest for justice.
Actually Dreyfus was tried and convicted again, and he was not exonerated until several years after Zola's death. Yet the tremendous challenge that Zola courageously undertook to right a wrong is a true story and portrayed fairly accurately. This film is a fine memorial to a great novelist, who worked so hard to reveal the truth about his times.