Wow, I loved this book! The three viewpoint women are strong interesting and each is very different from the others.  The history of the code breakers is fascinating.  It was fun to spot real people: Queen (then Princess) Elizabeth, Princess Margaret, Prince Phillip, Allan Turing, and more.  After I finished the book, I read the author’s note and found out that many of the characters were either real people or based on real people. 

Another plus IMO is that the two timelines are only a few years apart and eventually converge.  I am so tired of historical novels with a modern timeline.