Set before World Wat I, it is about the encryptors or ciphers that were used during that time. It is fictional, but some things are mentioned that are real, like the bombing of the Lusitania and the shooting of J. P. Morgan. That made the book more real to me.
Emma Shuster's father is killed and she is left alone. She has helped him with a code to be used by banks and one of his students is building a code machine. Lieutenant John Patterson is with her when she finds her father's body.
Emma moves to Virginia and works for the government de-coding messages from the German's. I did not realize there were so many ways to write a message in code and that was interesting. I also did not realize the German's came so close to the US before the war by sabotaging factories an ships.
The German's continue to try to find Emma and the machine. There is so much suspense and yes, another murder. I'll leave it at that because I don't want to tell the ending of the story and I did not read the last pages first. It is a wonderful book. I give Susan five stars.