1940. As England prepares to fight the Nazis, three very different women answer the call to mysterious country estate Bletchley Park, where the best minds in Britain train to break German military codes. But war, loss and the impossible pressure of secrecy will tear them apart. 1947. As the royal wedding of Princess Elizabeth and Prince Philip whips post-war Britain into a fever, Osla, Mab and Beth are reunited by a mysterious encrypted letter --- the key to which lies buried in the long-ago betrayal that destroyed their friendship and left one of them confined to an asylum. A mysterious traitor has emerged from the shadows of their Bletchley Park past, and now the trio must resurrect their old alliance and crack one last code together. But each petal they remove from the rose code brings danger --- and their true enemy --- closer.