The Quiet Librarian — Allen Eskens

After the murder of her best friend, a librarian's search for answers leads back to her own dark secrets in this sweeping novel about a woman transformed by war, family, vengeance, and love, from award-winning writer Allen Eskens.

Hana Babic is a quiet, middle-aged librarian in Minnesota who wants nothing more than to be left alone. But when a detective arrives with the news that her best friend has been murdered, Hana knows that something evil has come for her, a dark remnant of the past she and her friend had shared.
 
Thirty years before, Hana was someone else: Nura Divjak, a teenager growing up in the mountains of war-torn Bosnia -- until Serbian soldiers arrived to slaughter her entire family before her eyes. The events of that day thrust Nura into the war, leading her to join a band of militia fighters, where she became not only a fierce warrior but a legend -- the deadly Night Mora. But a shattering final act forced Nura to flee to the United States with a bounty on her head.
 
Now, someone is hunting Hana, and her friend has paid the price, leaving her eight-year-old grandson in Hana's care. To protect the child without revealing her secret, Hana must again become the Night Mora -- and hope she can find the killer before the past comes for them, too.