Kristin Hannah's The Nightingale is the story of two sisters in Nazi-occupied France in World War II and the different paths the occupation leads them on.

The older sister Vianne is a wife and mother who also teaches at a small school in the French countryside. Vianne is more conservative, seeking to hold on to the family home and to her family, including her husband who is fighting at the front. When the Nazis occupy France, a soldier named Captain Beck boards (forcibly) in Vianne's home. Her story mostly focuses on how she negotiates the complex relationship between herself and "the enemy." She finds Beck sympathetic; for example, he has a wife and children at home. Vianne's interaction with Beck suggests that war creates somewhat arbitrary divisions between people who might otherwise be friendly with each other. As such, the novel examines how war complicates personal relationships. Vianne's story also shows how war and discrimination can forge relationships, as she tries to help her best friend and her family who are Jewish. She even takes in her friend's child and raises him as her own. Vianne can be seen as a less heroic character than her sister Isabelle (the titular nightingale) because she dissuades her sister's rebellious activities, hoping to keep everyone safe. However, as the novel continues, Vianne becomes rebellious in her own ways. She kills Beck to protect Isabelle, and she helps smuggle Jewish children into a convent to keep them safe from the Nazis. Vianne's character evolution demonstrates the power of quiet, humble heroism and of the strength of love and community, even in the worst of circumstances.

Isabelle, on the other hand, is an overt rebel. The younger sister is outraged when the Nazis occupy France and wants to actively fight to preserve her nation. She becomes involved in an underground group and later moves to Paris, where she becomes "the nightingale." Her journey takes her to the borders of European nations as she leads fallen Allied soldiers away from the Germans and to safety. She repeatedly puts her life on the line for others, despite her older sister's warning, and at some points, blatant disapproval. Her involvement in the rebellion also reunites Isabelle with her estranged father. Their relationship repairs itself slowly as the two work together. It turns out that despite the resentment Isabelle harbors, she and her father have more in common than she might have guessed. Their interaction also shows that forgiveness is possible, and that dire circumstances can bond two people who may have otherwise never reunited.

The Nightingale is a novel about different kinds of heroism and the way war both destroys and forges relationships. It's a deeply moving historical novel.