Sarah’s Key is a novel told from multiple perspectives and points in time. At the outset of the novel, there are two narratives occurring: one in 1942, and the other in 2002. In 1942, Sarah’s family is taken, along with a host of other Jewish families, in the Vel’ d’Hiv’ roundup by the French police. Before they leave their home, Sarah hides her little brother, Michel, in a secret cupboard in the house. She grabs the key to the cupboard, promising to come back to let him out soon.

Meanwhile, in 2002, Julia, an American living in Paris, renovates an apartment owned by her husband’s grandmother, Mamé. The plan is to move in with her husband, Bertrand, who stays mostly absent from the lives of Julia and her daughter, Zoë. Julia works on a story for an American newspaper about the centennial of the Vel’ d’Hiv’ roundup of Jews in Paris. Julia is warned off of the story by many people, however, including her own family, because the French are ashamed about being involved in such an atrocity.

Meanwhile, in 1942, Sarah and her mother and father are taken to the holding stadium known as Vel’ d’Hiv’. Eventually, her father and mother are taken to Auschwitz, while Sarah is left behind. She fears that she’ll never be able to get back to her apartment to let her brother out. Along with another little girl, Sarah convinces a policeman, whom she knows from before the war, to let them out. She escapes finally to an elderly couple’s home in Orleans.

Julia, in 2002, follows the story of the Vel’ d’Hiv’ roundup, much to the chagrin of her husband and others. She learns about the deportation of the Jews by the French police, and she discovers that a family of French Jews once occupied her own apartment on the Rue de Saintonge. Mamé and her family, like other families, took the apartments once the Jewish families were deported. Again, she is asked to stop looking into this by her husband and his father, Edouard. Julia is shocked. She is shocked again by the news that she is pregnant.

Here, the stories begin to merge, as Julia learns more about the history of the apartment from her father-in-law, Edouard. He remembers Sarah returning to the apartment with the elderly couple to look for her brother, whom they found dead in the cupboard. He felt that she always blamed them for that. He found some papers showing that his father used to send money to the elderly couple for the care of Sarah.

Bertrand does not want a baby and wants a divorce, should Julia decide to go through with the pregnancy. Julia is torn. She continues, however, to research the girl Sarah and what happened to her. She discovers that Sarah moved eventually to the United States. Julia goes there to investigate. Julia finds out that Sarah and her husband might be living in Connecticut. When she speaks to the daughter, however, she finds out that Sarah’s husband has remarried, and that Sarah died in a car crash. Julia is dismayed. They say that she had a son, William, who lives in Italy.

Julia and Zoë, Julia’s daughter,go to Italy to find William. They meet him in a café. William is too shocked by this news and orders Julia to leave him alone. Juliapasses out due to issues stemming from her pregnancy. When she comes to, she and the baby are okay. Bertrand remains distant. William arrives to learn more about his mother and go on a journey of discovery. Julia has feelings for him.

Years later, Julia, Zoë and the little girl live in New York City. Julia is single again and struggles to find anything meaningful with anyone. She thinks about William often. After Googling him, she discovers he lives in New York City. One day, he calls her. They meet. William thanks her for helping him to know his mom, Sarah. They embrace. She says that she’s named her daughter Sarah.