2003. The United States and Britain are preparing to intervene in Iraq because the Bush administration is claiming, without plausible proof, that Saddam Hussein has weapons of mass destruction. Katharine Gun, a British intelligence employee at Government Communications Headquarters (GCHQ), receives a secret memo in her e-mail indicating that the United States is seeking Britain's help in gathering incriminating information on certain UN Council delegates in order to force them to vote in favour of the invasion. If they vote against, they will be publicly disclosed. Stunned, Gun is reluctant to reveal the scheme behind this illegal intervention. Despite this, she anonymously sends the memo to the press in an attempt to prevent the war, which looks to be unnecessary and with disastrous consequences. But by choosing to expose this vast political conspiracy, the whistleblower puts her life, her marriage, her freedom and her sense of patriotism at risk. For her decision is considered treason in the eyes of the British secret service...