The cryptographer's dilemma. (Heroines of WWII, #1.)
(Book)

FBI cryptographer Eloise Marshall is grieving the death of her brother, who died during the attack on Pearl Harbor, when she is assigned to investigate a seemingly innocent letter about dolls. Agent Phillip Clayton is ready to enlist and head oversees when asked to work one more FBI job. A case of traitorous messages disguised as correspondence about dolls should be easy, but not so when the clues take Eloise and Phillip on a cross-country trek that has them both confronting past demons and an unmistakable attraction. Eloise believes the letters refer to classified intel about U.S. warships, but can she prove it in time to catch the spy? Or, before she and Phillip are permanently separated?