Lilac Girls by Martha Hall Kelly

Manhattan, 1939. New York socialite Caroline Ferriday's biggest problem is resisting the advances of a married actor. Across the Atlantic Kasia Kuzmerick, a Polish Catholic teenager, is affected when Germany declares war on Poland. As tensions rise Caroline's interest in aiding the war effort in France grows; she hears about the dire situation at the Ravensbrück all-female concentration camp. Kasia's carefree youth is replaced by a fervor for the Polish resistance movement. Through Ravensbrück-- and the horrific atrocities taking place there told in part by an infamous German surgeon, Herta Oberheuser-- the two women's lives converge in unprecedented ways. Read a sample.