The story alternates between the war and 1947, just before Princess Elizabeth's marriage to Prince Philip. Three women work at Bletchley Park breaking Axis codes during the war, and hate each other bitterly by 1947. One of them is in an asylum by that point, and thinks she was put there by a Bletchley Park traitor. We see how they came together, how they fell apart, and wonder whether they'll come together by the end. While the plot isn't a masterpiece, it is good enough to not be in the way of what are extremely rich characters and amazing historical detail.