In 1894, Alfred Dreyfus, captain in the French army, is found guilty of high treason for passing military secrets to the German Empire.

One year later, officer Georges Picquart, Dreyfus' former teacher, is appointed head of the secret service section in the French army (Deuxième Bureau).

Picquart discovers that the so-called bordereau, the document that ostensibly proves his guilt, was not written by Dreyfus, as the graphologist Alphonse Bertillon had claimed, but by another soldier: Major Ferdinand Walsin Esterhazy.

Picquart is convinced of Dreyfus' innocence and tries to reopen the trial to exonerate him and arrest Esterhazy, but meets the opposition of his superiors: admitting Dreyfus' innocence would result in a great scandal that would lead to the discovery of corruption in the army, while the man, as a Jew, is the perfect scapegoat.

However, he manages to return and tell everything to his friend, the lawyer Louis Leblois, who begins to organise a committee for the rehabilitation of Dreyfus, involving his colleague Fernand Labori, members of the Parliament and intellectuals, including the famous author Émile Zola.

Picquart's insubordination leads to his arrest, but on the same day Zola publishes in the newspaper L'Aurore the article entitled J'accuse, where he fiercely criticises the irregularities of the trial of Dreyfus and exposes all the people involved in the case.

Zola, on a complaint from the government, is tried for defamation and, due to the false declarations made in the courtroom by the soldiers called to witness, the writer is sentenced to one year in prison.

While the whole of France is divided between innocent and guilty parties, the intellectuals signing the pro-Dreyfus petition are targeted for popular hatred.

Later, after losing a duel against Picquart, Lieutenant Colonel Hubert Joseph Henry, who had testified against Dreyfus, admits he perjured himself, and dies shortly after, apparently by suicide.

Shortly before the decisive hearing, the lawyer Labori suffers an assassination attempt and is unable to defend Dreyfus.

Dreyfus asks him for an audience and protests because the years in which he has unfairly served his sentence have not been recognised, preventing him from reaching the rank of lieutenant colonel.

Robert Harris was inspired to write the novel by his friend Polanski, who has long had an interest in the Dreyfus affair.

[...] A man who commits a crime of this size who is then condemned, and the victim considers herself satisfied with the compensation is difficult for me to judge...

[35][36] Martel later clarified her comments, stating: "According to some reports after today's press conference, I believe my words were deeply misunderstood.

"[37] Alberto Barbera, the festival director of Venice, had previously defended the film being in the lineup, stating: "We are here to see works of art, not to judge the person behind it.

"[41] In November 2019, five days before the official release of An Officer and a Spy in France, Polanski faced accusations of rape by a French woman, Valentine Monnier.