It's January 2003, and US President George W. Bush is working closely with British Prime Minister Tony Blair in his effort to make a case for the invasion of Iraq to the United Nations. Katharine Gun (Knightley) is a Mandarin translator working in a cubicle at GCHQ; her husband Yasar (Bakri), a Kurdish refugee, is working in a cafe while he tries to get permanent UK residency. The news irritates her, but it's just a job.
That is until she reads an email to GCHQ from Frank Koza, the chief of staff for regional targets at the NSA. In it, Koza asks GCHQ to help gather blackmail material on the UN delegations for six swing-voting nations on the UN Security Council. Katharine is furious at the unlawful order, and through a friend in the peace movement, makes the decision to leak the email to the press. Observer reporter Martin Bright (Smith) gets ahold of it and publishes the memo after verifying Koza's existence.
In short order a mole hunt starts up at GCHQ, and Katharine Gun, charged with a violation of the Official Secrets Act, finds herself in need of a lawyer (Fiennes).
This film contains examples of the following tropes:
- Adaptation Name Change: The real Katharine Gun's husband is named Suat Gün. No explanation is given for the change to "Yasar". (Also, the real Katharine Gün uses an umlaut on her married name, but the press left it off, as does this film.)
- Amoral Attorney: Prosecutor Ken Macdonald is, like the rest of the British government, Just Following Orders. At the end of the film, Ben Emmerson (Fiennes) calls him out on leaving Katharine in suspense for most of a year, only to abruptly drop all charges in the first five minutes of the trial after Ben subpoenas a government legal opinion that the Iraq War was unlawful.Ben: Do us a favor, Ken. Go and fish somewhere else.
- Blackmail: The NSA essentially tries to get GCHQ to help them blackmail the UN delegations from Angola, Bulgaria, Cameroon, Chile, Guinea, and Pakistan into supporting a resolution that would legalize the invasion of Iraq.
- Bunny-Ears Lawyer: Rhys Ifans's character, Ed Vulliamy, is an erratic, profane, and scruffy investigative reporter who is adamant that the imminent Iraq War is a sham. He's also the guy who confirms despite the NSA's best efforts that Frank Koza exists and authored the memo Katharine leaked.
- Citizenship Marriage: Yasar Gun was facing deportation when they married, but they're legitimately in love.
- An Immigrant's Tale: Yasar is trying to get permanent residency in the UK, but is nearly deported two thirds of the way through the film to punish Katharine for leaking the memo.
- Morton's Fork: The Official Secrets Act continues to cause problems for Katharine even after her original charge for leaking the NSA memo: she's informed by a Scotland Yard detective after she consults Ben Emmerson at Liberty that discussing the details of her potential charges with an attorney counts as an additional OSA violation in its own right, even though she has a right to legal representation under British law. In other words, if she gets an attorney she takes two OSA counts instead of one, but if she doesn't, she almost certainly goes to prison. Katharine turns it back on him by promising that she won't discuss the memo with anyone else unless she's charged, and her lawyer Ben Emmerson is able to get the gag order lifted before the trial.
- Spanner in the Works: The Observer's front-page story revealing the US-British plot to influence the UN vote is spoiled because a copyediting intern ran the story, including the reproduced memo, through spell-check, changing the American English spellings to British English. This is pretty close to what actually happened.
- Stock Footage: The news coverage used in the film is all archival video. There's even Stock Footage of the real Katharine walking out of the courthouse after her acquittal.
- To Be Lawful or Good: The dilemma of Gun and the other GCHQ staff: obey the law and see Britain help start an illegal war that (as we now know) will kill hundreds of thousands of people? Or leak the memo and risk prison and the loss of her husband's immigration status? The others Just Follow Orders; Katharine blows the whistle.