Deborah Lipstadt is an American professor of Holocaust studies whose speaking engagement is disrupted by David Irving, a British writer on Nazi Germany. He files a libel lawsuit in the United Kingdom against Lipstadt and her publisher for declaring him a Holocaust denier in her books. As the burden of proof in UK libel cases lies with the defendant, Lipstadt and her legal team, led by Anthony Julius and Richard Rampton, must prove that Irving lied about the Holocaust.
To prepare their defence, Lipstadt and Rampton tour the site of the former Auschwitz concentration camp in Poland. The historian Robert van Pelt explains the operation of the gas chambers, while the research team subpoenas Irving's extensive personal diaries. Lipstadt is annoyed by Rampton's apparently disrespectful questions; the team reduces her involvement in the case, arguing that she harms its chances of success. Members of the British Jewish community plead with her to settle out of court to avoid creating publicity for Irving. However, her team has a promising start when they persuade Irving, by appealing to his ego, to agree to a trial by judge instead of a jury, which he could have manipulated to his advantage.
Irving conducts his own legal representation, facing Lipstadt's legal team. Irving endeavours to twist the presented evidence for the defence. Lipstadt is approached by a Holocaust survivor who pleads for the chance to testify, but Lipstadt's legal team insists on focusing the trial on Irving.
Irving tries to discredit van Pelt's evidence for the existence of gas chambers at Auschwitz, claiming there were no holes on the roof for the Zyklon B gas crystals to be introduced. His slogan "no holes, no Holocaust" dominates the media coverage. Furious, Lipstadt demands that she and the Holocaust survivors be allowed to take the stand. Julius angrily counters that Irving would only humiliate and exploit a survivor on cross-examination, as he has in the past. Rampton visits Lipstadt at her home to explain his approach and earns her trust. In court, he subjects Irving to a skillful cross-examination and exposes his claims as absurd, while expert testimony from respected scholars such as Richard J. Evans expose the distortions in Irving's writings.
As the trial concludes, the judge, Charles Gray, worries the defence by suggesting that, if Irving honestly believes his own claims, he cannot be lying as Lipstadt asserted. Gray eventually rules for the defence, however, convinced of the truth of Lipstadt's portrayal of Irving as deceitful. Lipstadt is hailed for her dignified demeanour, while her legal team reminds her that, despite her silence during the trial, it was her writing that countered Irving's lies and provided the basis for the victory. At a press conference, Lipstadt praises her lawyers for their strategy.
