The Crimson Cipher — Susan Page Davis

A female Navy cryptographer seeks to save lives...and uncover her father's killers.
In 1915, German sympathizers escalated acts of sabotage in the United States to keep the nation from joining in the war. Following the mysterious murder of Emma Shuster's father, Lt. John Patterson invites Emma to become a Navy cryptographer because of the expertise she gained in helping her father develop a cipher system. Emma finds new strength in her faith as she strives to outwit her adversary, known only as Kobold - German for goblin. Can Emma and John find love in the midst of turmoil as America plunges toward war?