Hannah Martel, a young Jewish woman, flees Germany to escape the Nazis. She takes up residence in Belgium, where she reconnects with her cousin, Lily, and joins the Sapphire Line, an underground resistance network seeking to transport downed British airmen across the Pyrenees. When Hannah makes a colossal blunder that leads to the arrests of Lily and her family, she must find a way to rescue them from a train bound for Auschwitz. Pam Jenoff excels in writing about the often fraught relationships between family members. The narrative moves briskly towards a tense denouement.