The True Story Behind 'Denial' : Inside a Historian's Incredible Fight to Prove a Holocaust Denier Wrong

There aren’t always two sides to a story.

“There are certain things that are true,” Deborah Lipstadt tells PEOPLE. “And the Holocaust is one of them.”

The historian was the defendant in a British libel lawsuit brought by Holocaust denier David Irving when she exposed his falsification of history in her book Denying the Holocaust. The new film Denial, starring Rachel Weisz and directed by Mick Jackson, recounts the acrimonious trial.

“When I first heard about Holocaust denial, I laughed. I thought, ‘This is ludicrous. These are just theories. Who would take them seriously?” says Lipstadt, 69. “Then I began to see there were people who began to think, ‘Well, maybe there’s something to it.’ ”

Her passion for speaking out against lies and standing up for the truth compelled Lipstadt to write and publish her book Denying the Holocaust: The Growing Assault on Truth and Memory in 1993, which was one of the first full-length examinations of Holocaust denial. In it, she calls Irving both a “liar” and “falsifier of history,” and accuses him of “taking accurate information and shaping it to confirm his conclusions.”

Lipstadt, who is portrayed by Weisz in the film, says she was shocked when Irving sued her.

“Not because what I wrote wasn’t strong, but other people had written far worse about him before,” she says.

Irving was a well-known military historian who claimed that the Final Solution took place without Hitler’s knowledge and that the gas chambers and extermination camps did not actually murder millions of Jews.

“This man was spewing lies, it makes your blood boil — spewing lies, anti-Semitism and sneering contempt for Jews.”

And because of the way English libel law works, the burden of proof was put on the defendant, rather the plaintiff. In court, Lipstadt had to prove that Irving was purposefully and maliciously spreading lies about the Holocaust.

“It was a very strange experience because my work was at the center of the whole fight — what I had written, my reputation, my future,” she says. “I had to remain silent because the lawyers determined that it was my book that was on trial — there was nothing I could add.”

But when it came time for Lipstadt’s team (which included Princess Diana’s former divorce attorney Anthony Robert Julius) to present their case against Irving, all the proof was in his work.

“We followed his footnotes,” she explains. “Some people say follow the money — we followed his footnotes back to his sources. What we found was that in every single case, he would twist something. We showed numerous instances where documents just were falsified.”

“At one point he was arguing in favor of the document and the judge just looked at him and said, ‘Mr. Irving, it doesn’t say that,’ ” she recalls. “We knew we had the judge at that point.”

The judge produced a written judgment more than 300 pages long detailing Irving’s systematic distortion of the historical record.

“It took a long time. It was hard, it was tough and it caused a lot of pain, but it was a tremendous win and a tremendous moment,” she says.

“It’s a story of a great victory, but it’s also a real tragedy.”

Denial is in theaters now.