As the Nazis try to smash and conquer the free world, three women answer the call to do their part at Bletchley Park. These women are in charge of deciphering Nazi codes, if they succeed, they will change the course of history. Mab, who comes from a poverty ridden background. She wants to defeat Hitler, and find a rich husband while she does so. Osla is a wealthy, society sweetheart who would rather use her formidable intelligence to help the allies than court a prince. Beth is a shy, unmarried woman who will use her ability to solve puzzles to help the war effort and find herself at the same time. But these three friends become enemies during the course of their time at Bletchley. Can an encrypted letter and a royal wedding 3 years after the end of the war reunite them?