The movie tells the story of Katharine Gun (played by Keira Knightley), a translator with the U.K.’s GCHQ who, in 2003, leaked top secret documents to journalist Martin Bright (Matt Smith) that revealed that the American government’s plans to apply pressure on members of the U.N. Security Counsel to pass its war resolution.

In the film, when Gun is sent an email from someone high up in the U.S. government that reveals the U.S. covert plan, she decides to leak it to Bright, who works for the British newspaper The Observer, which then publishes it on their front page. However, when her friends start being interrogated about the leak, Gun confesses to being the whistleblower, leading to her being arrested and taken to court for breaching the Official Secrets Act. But when Gun’s lawyers threaten to question the U.K. Attorney General Lord Goldsmith about Britain’s involvement in the Iraq war, the government drops their case against Gun.

Official Secrets is, for the most part, a historical account of these events in 2003, but as with nearly all films based on a true story, some things have been changed to aid the drama of the narrative. To separate fact from fiction, Newsweek spoke to the real Gun and Bright, as well as Official Secrets director Gavin Hood.

Warning: The following contains spoilers for Official Secrets.

“Obviously, we are compressing a story that took place in real life over a period of a year into two hours. So right there, you are pulling out the highlights,” said Hood of the key issue with making Official Secrets.

This meant that a lot of the things that we see Gun go through in the film actually took far longer in real life. For example, a scene where Gun tries to get her husband out of an immigration detention center actually played out over three days during which she did not know where he was.

The real-life Gun said: “The attempt at deportation kind of spiked my stress level again for another period of my life.” However, Gun added that this was nothing on the anxiety she felt when the memo she had leaked ended up on the front page of The Observer, which she called “the most stressful memo of my life.”

Speaking to Gun, and seeing her in archival footage at the end of the film, it is clear that Knightley didn’t try to emulate the look or sound of the real-life Gun. Hood said that this was a purposeful choice by Knightley. “We started wondering whether we should do the blonde hair and the glasses and wondering about prosthetics, but one point Keira said to me, ‘You know, the last thing I want is the audience to say, ‘Oh, I don’t know if I like her blonde,’” said Hood. “And she then said: ‘My way into this is what would I as the unadorned, no-makeup, no-fancy-edges Keira Knightley… what would I feel like if this memo landed on my desk?’”

In one pivotal scene in the film, all of Gun and Bright’s work is nearly undone by one mistake, as a member of The Observer team accidentally changed the American spelling of the memo into British spelling, something The Drudge Report then used to discredit the memo. “That really happened,” Hood confirmed, though it did not go quite as it is shown in the film.

As Bright noted, however, what we see in the movie is close to the real events. He said: “Very close. Unfortunately. Not mine or The Observer’s finest hour, has to be said. The poor woman is based on a real person. This was her first or second week at the paper. So it was a pretty awful thing to happen to her. And it’s also true that we were then attacked by the Drudge Report for what would now be called ‘fake news.’”

The reality was not nearly as dramatic as in the film, where Bright and his editor are together in a newsroom when the mistake is revealed, leading to them being dropped from interviews with a number of international news outlets. In real life, “the spellcheck largely happened through a series of phone calls,” according to Bright, “because on a Sunday newspaper we don’t work on a Sunday, and we don’t work on a Monday.”

Bright noted that apart from some small flourishes to heighten the drama, he didn’t think Official Secrets had “any genuine liberties taken with the truth.”

“I think Gavin had a really difficult time telling this story because it doesn’t fit into a normal sort of storytelling mode,” said Gun. “One of the things that we discovered quite early on when he was interviewing me was that a lot of stuff was just happening in my head. It was what I was thinking, what I was feeling. And he kept thinking, ‘How am I going to portray this?’”

“The scene where all of us receive this email and we’re discussing the memo, that never happened. [In real life] I saw the email, I immediately thought, ‘Oh, my God, this is shocking.’ But there’s no way I would have expressed that to any of my colleagues,” Gun explained. “I think part of the reason Gavin included it was just to kind of share that thought process.”

The difficulties of translating Gun’s story also made writing the climax of the film tricky. Following the trauma inflicted on Gun, the U.K. Attorney General dropped the case against her with no warning.

“You get to the end, and there’s this court case. If I was writing this as fiction, I need a much longer court case, right? Well, you don’t have one and get that almost anti-climactic moment that is a punch in the gut,” said Hood. “On the one hand, she’s free. On the other hand, she and Ben, to this day, feel they never got their day in court.”

Hood added: “You know, to this day, I mean, the real journalistic question is, who would like to go and really press Lord Goldsmith and Ken McDonald for the reasons why they really dropped their case?”

Official Secrets is in theaters now.