Julia is an American journalist who has lived in Paris for fifteen years. She works for Seine Scenes magazine and receives an assignment to write an article on the sixtieth commemoration of the Vel' d'Hiv' roundup. Though she loves France, she frequently feels like an outsider, a sentiment her husband often reinforces. She investigates the history of the apartment her family is renovating, deeply affecting her personal life.

Sarah is a young Jewish girl living in Paris during World War II. When the police arrive for the Vel' d'Hiv' roundup, she hides her little brother in a secret wall cupboard to protect him. Enduring horrific conditions in the holding stadiums and internment camps, she clings to the brass key, driven by her desperate promise to return to the apartment and free him.

Bertrand is Julia's fashionable French husband and an architect. He looks down on Julia's American background and grows frustrated by her persistent investigation into the Jewish family who previously occupied their new apartment. He heavily opposes the idea of having another child, bringing their marital problems to the surface.

Edouard is Bertrand's father and Julia's father-in-law. Initially projecting a cold and reserved demeanor, he guards the difficult secrets of his family's history from the 1940s. When Julia uncovers the truth, Edouard finally opens up, revealing his guilt over what happened to Sarah Starzynski when he was twelve years old.

Zoë is Julia and Bertrand's perceptive teenage daughter. She takes an active interest in her mother's investigation into the Vel' d'Hiv' roundup and the family who previously occupied their home. She acts as a mature support system for Julia during her marital struggles.

William is an American man living in Italy. He is completely unaware of his mother's traumatic childhood in France during World War II. When Julia approaches him with the historical evidence, he reacts with shock and defensiveness, struggling to reconcile this dark history with the mother he knew.

Michel is Sarah's beloved younger brother. During the 1942 roundup, he relies on his sister's quick thinking and hides in the locked cupboard. His safety becomes Sarah's singular motivation for escaping the internment camps and returning to Paris.

Also known as Madame Tézac, Mamé is Bertrand's grandmother. She resides in a nursing home and suffers from Alzheimer's disease. In July 1942, her family moved into the Rue de Saintonge apartment shortly after the Starzynski family was forced out.

Jules is an elderly French farmer in Orléans. Despite the immense danger of harboring Jewish fugitives during the war, he takes in Sarah and Rachel, offering them food and shelter when they are completely desperate.

Geneviéve is Jules's wife. She is a practical and maternal woman who helps nurse the sickly escapees. She later writes a letter documenting Sarah's hardened spirit and difficult recovery after the war.

Rachel is a young Jewish girl imprisoned alongside Sarah. She partners with Sarah to slip through the barbed wire of the camp. After their escape, her health deteriorates rapidly, putting them both in a vulnerable position.

Gaspard is the grandson of Jules and Geneviéve Dufaure. As an older man in 2002, he serves as a vital link for Julia, providing memories and documents about Sarah's time with his grandparents and her eventual departure to America.

Joshua is Julia's boss at Seine Scenes magazine. He tasks her with writing an article on the sixtieth commemoration of the Vel' d'Hiv' roundup, setting her investigation into motion.

Charla is Julia's younger sister, an athletic attorney living in the United States. She acts as Julia's long-distance confidante, helping her track down contacts in America and offering emotional support regarding her pregnancy and marital issues.

Bamber is a photographer working with Julia at the magazine. He accompanies her to various historical sites related to the deportations, acting as a sounding board as she processes the grim history.

Monsieur Starzynski is Sarah and Michel's father. During the roundup, he is separated from his family at the holding camp. Before his arrest, he used to answer Sarah's questions but remained silent about the yellow stars they were forced to wear.

Madame Starzynski is Sarah's mother. She attempts to plead with the police, arguing that Sarah is a French citizen. In the holding camps, she grows silent and ages visibly under the strain before being permanently separated from her daughter.