2003, on the eve of the American intervention in Iraq. Katharine Gun, a British intelligence officer, receives a note from the NSA: the United States seeks Britain's help in gathering compromising information on certain members of the UN Security Council to force them to vote in favour of the invasion. Gun decides to release the memo to the press to prevent war. By choosing to expose this vast political conspiracy, the whistleblower risks everything: her life, her family, her freedom…