New York socialite Caroline Ferriday has her hands full with her post at the French consulate. But the privileged life to which she is accustomed is turned upside down when her lover suddenly and suspiciously disappears.
An ocean away in Germany, indoctrinated young Herta Oberheuser is desperate to begin working as a doctor. She replies to an advert for a government medical position, yet only upon arrival does she discover the true extent of her horrifying new role.
As the war advances, Polish teenager Kasia Kuzmerick is drawn deeper into the underground resistance movement. In a tense atmosphere of watchful eyes and suspecting neighbours, one false move can have dire consequences.
Then the unthinkable happens: Kasia is sent to Ravensbrück, the notorious Nazi concentration camp for women where Herta now works, and her life is transformed into a desperate attempt to survive.
As the women's stories coincide and span decades and continents - from New York to Paris, Germany, and Poland - the devastation of Ravensbrück is ever-present, as Kasia and Caroline strive to bring justice to those history has forgotten...