The author of The Huntress and The Alice Network, both of which were bestsellers in both the New York Times and USA Today, is back with another heart-stopping World War II novel about three female code-breakers at Bletchley Park and the spy they must find when the war is done.

1940. At a time when England is getting ready to fight the Nazis, three women who couldn't be more different answer the call to go to the secretive country estate known as Bletchley Park. There, the greatest minds in Britain train to break German military codes. Osla, a vivacious debutante, is the girl who appears to have it all—beauty, wealth, and the charming Prince Philip of Greece sending her roses—but she has a burning desire to demonstrate that she is more than just a society girl, and she puts her fluency in German to use as a translator of decoded enemy secrets. Imperious Mab, a self-made woman who came from a poor background in the east end of London, works the famed codebreaking machines while covering up ancient wounds and searching for a partner who will be socially advantageous. Both Osla and Mab are quick to spot the promise in a local village spinster named Beth, whose timidity belies a tremendous skill with puzzles. Soon after, Beth spreads her wings as one of the Park's few female cryptanalysts, and Osla and Mab are impressed by her. But, conflict, loss, and the unbearable burden of the secret will ultimately cause the three to become estranged from one another.

1947. At the same time that the royal wedding of Princess Elizabeth and Prince Philip is sending post-war Britain into a fever, three former friends who have turned into enemies are brought together by a mysterious encrypted letter. The key to deciphering the letter is buried somewhere in the long-ago betrayal that ended their friendship and caused one of them to be institutionalized. As a result of the appearance of a shadowy traitor from their time spent at Bletchley Park in the past, Osla, Mab, and Beth now need to resuscitate their previous alliance in order to break one more code together. Yet with each petal they peel from the rose code, they bring the threat, as well as their real adversary, closer...