This is the story of Anne Keyes (played by Romola Garai), the adopted daughter of Sir Alexander MP (Bill Nighy). The movie begins with a boy, in present time, who asks two old men, who knew Anne Keyes, what had happened to her in the eve of WW2.
Anne Keyes, an actress, lives happily with her family: Sir Alexander, his wife, and his two children: Ralph and Celia. She also has a fiancé, Lawrence, whom she loves. Things are well until that dinner in their country house, when Hector, a young MP, meets Balcome. Hector expresses his opinion, in which he disagrees with some people who wants to make a deal with Hitler. For some, the horror of WW1 is still fresh in their memory and they try to avoid war. It's obvious that Balcome, who works for the secret service, doesn't agree with Hector. A couple of days later, Hector is found dead, probably suicide.
Anne finds a recording in her father's store-room which contains a telephone conversation, where Hector was being threatened. Could it be possible that he has been murdered?
For Anne, the whole thing is a nightmare. First, she lost baby Oliver. She is falling asleep and someone has taken him, and returns him. Next, she asks a fellow actor to listen to the recording and soon he is found dead. The worst for her is when Lawrence is also dead and she finds that her family know about the conspiracy from the start.
What is scary here, is the knowledge how powerful the secret service is.