Caroline Ferriday is a former actress from a wealthy and predominant family who is working with the French Consulate in New York City.
Kasia, along with her mother and sister, have been caught working for the underground resistance in Poland. They are sent to Ravensbruck and are subjected to torturous experiments. These women were called 'rabbits' because they would hop about on their healthy leg, and they were the Nazi's experimental 'rabbits'.
Herta Oberheuser is a young German doctor, the only female physician at Ravensbruck. She is part of the group of doctors responsible for the horrific experiments performed on the Polish women with the goal of learning how to best heal the German soldiers.
I really enjoyed Hall Kelly's author's note at the end of the book. Her research is incredibly impressive and thorough. This provides the reader with a deeper understanding and connection with the characters, especially when you find out that they actually existed.