Sarah’s Key tells the intertwined stories of Sarah Starzynski, a ten-year-old Jewish girl living in Paris during World War Two, and Julia Jarmond, a forty-five-year-old American-born journalist living in Paris in 2002. For the first third of the novel, Sarah’s and Julia’s stories are intertwined, while the remainder of the book focuses on Julia’s story.
Sarah’s story begins in July of 1942. Along with her mother and father, ten-year-old Sarah is rounded up by the French police as part of a mass arrest of Parisian Jews known as the Vel’ d’Hiv’ roundup. Sarah’s younger brother, four-year-old Michel, convinces Sarah to lock him in the secret cupboard where the siblings often read and play together. Sarah, not realizing the implications of her family’s arrest, pockets the cupboard key and promises to return for Michel soon. As the Starzynski family is escorted out of their apartment building on the rue de Saintonge, Sarah infers from the concierge’s conversation with the police that she, Madame Royer, was the one who sold out Sarah’s family to the police.
After being held in a garage on the rue de Bretagne, where she recognizes fellow detainees and neighborhood policemen alike, Sarah and her family are moved to the Vélodrome d’Hiver, an indoor cycling track, where they are held without food, water, or sanitation for several days along with thousands of other Jewish families. By this point, Sarah has shown the key to her mother and father and both parents have reacted in despair, realizing that Sarah has unwittingly left her brother to die. Sarah, however, vows to find a way to return to her brother. Eventually, Sarah and her parents are taken to a railway station and transported away from Paris to the Beaune-la-Rolande internment camp. Upon their arrival, the men are separated from the women and children, and shortly thereafter the French police running the camp violently separate the mothers and children, as well. Left alone with the other children, many of them very young, Sarah befriends a girl named Rachel. Sarah and Rachel agree to escape from the camp, which they do successfully after Sarah persuades the policeman who catches them crawling under the barbed wire fence to let them go.
Sarah and Rachel walk for miles across the countryside, hiding in the forest and eventually in a dog shed. It is here they are discovered by an elderly man named Jules Dufare. Jules and his wife, Geneviève, feed and shelter Sarah and Rachel. However, when Rachel becomes dangerously ill with dysentery, Jules and Geneviève decide they must take the risk of calling a doctor. As a precaution, they order Sarah to hide in the basement, as her shaved head will give her away as an escapee. The doctor visits Rachel and leaves only to return with several German officers. Sarah manages to stay safe hiding in the cellar, but the Germans take Rachel away with them and Sarah never hears of her again. Devastated by Rachel’s capture and the loss of both her parents, Sarah resolves to return to Paris to find Michel. Jules and Geneviève decide to accompany her.
By bribing a policeman and pretending that Sarah is Jules and Geneviève’s granddaughter, the three are able to make their way back into occupied Paris. There, Sarah leads the way back to her apartment, where she is greeted by a young boy her age (Edouard Tézac) who is now living there with his family. Sarah forces her way into the apartment and unlocks the secret cupboard with the key she has kept safe all this time. Inside she finds her brother’s blackened, dead body and, overcome by grief, she collapses screaming. Sarah’s story leaves off here, and the reader learns further details of Sarah’s life only via Julia’s story.
Julia is an American living in Paris with a French husband, Bertrand Tézac, and an eleven-year-old daughter, Zoë. At the beginning of her story, Julia is planning to move into the apartment in Paris formerly belonging to Bertrand’s grandmother, known affectionately to the family as Mamé. While Julia has never felt accepted by her husband’s family, she enjoys a close relationship with Mamé, whom she visits weekly at the nursing home. While touring the apartment, Julia receives a call from her boss, Joshua, asking her to come into work. Once there, Julia receives an assignment to write an article about the Vel’ d’Hiv’ roundup, which will be commemorated in a few months. Julia is only vaguely familiar with this historical event, but she eagerly begins researching. Soon, she has become obsessed with the tragic deaths of the thousands of children arrested as part of the roundup. She tries talking about the topic with her husband, but Bertrand is dismissive, telling Julia no one cares about the roundup up and, thus, no one will read her article. It is revealed that Julia is hoping for a second child, but that several early miscarriages and a difficult pregnancy with Zoë have limited her options.
Through research, interviews, and a discussion with Mamé, Julia learns that the apartment she will soon move into formerly belonged to a Jewish family arrested during the roundup. She soon receives a call from her father-in-law, Edouard, forbidding her from discussing the topic further with Mamé, which only piques her interest. At this time, Julia discovers she is pregnant. Although she is elated, Bertrand insists she must have an abortion because another baby would “kill” him. During this conversation, it is revealed that Bertrand formerly had a mistress by the name of Amélie.
Helped by a local expert, Franck Lévy, Julia learns that the family who used to live in Mamé’s apartment was the Starzynskis. While Wladyslaw and Rywka, Sarah’s parents, are known to have died at Auschwitz, Sarah’s fate is unclear from the written record, and Julia becomes determined to track her down. She makes visits to two internment camps and continues researching, but is unable to learn anything until Edouard reveals that he was present when Sarah returned to the apartment on rue de Saintonge. Edouard’s father, André, had forbidden young Edouard from speaking of Sarah’s visit to his mother, Mamé, who was not at home that day. André also left some confidential papers in a safe at his death, and both Julia and Edouard become excited by the possibility that these papers might reveal something about Sarah’s fate. Upon examining the papers, Julia learns that André Tézac sent the Dufares money every month for ten years to help provide for Sarah, who continued to live with Dufares after the war.
By this point, the Vel’ d’Hiv’ commemoration has arrived. It is the same day that Julia is scheduled to have an abortion. At the clinic, Julia receives a phone call from Nathalie Dufare, Jules and Geneviève’s great-granddaughter. Elated by this development, Julia realizes she does not want the abortion, and abruptly leaves the clinic. By meeting with Gaspard Dufare, Nathalie’s grandfather and Jules and Geneviève’s grandson, Julia learns that Sarah left France in 1952, at the age of twenty. She moved to the United States and never contacted the Dufares again after 1955, when she wrote to say she was marrying an American.
Having essentially cut off communication with Bertrand, and still dead-set on finding Sarah, Julia soon leaves for the States with her daughter Zoë in tow. With the help of her sister, Charla, who is an attorney, Julia locates the house of Sarah’s husband, Richard Rainsferd, in Connecticut. She arrives there and meets a woman whom she initially thinks is Sarah, but who is actually Richard’s second wife. Sarah, Julia learns, died in a car crash in 1972 at the age of forty. Julia is stunned but remains hopeful upon hearing that Sarah and Richard have a son named William who now lives in Italy. Julia and Zoë fly to Italy to look up William, whom they are able to convince to meet with them. In this conversation, it becomes clear that William knows nothing of his mother’s past. After Julia shows him a photograph of Sarah wearing a yellow star, William becomes angry and instructs Julia never to contact him again. As she and Zoë leave to return to their hotel, Julia finds blood on her skirt and passes out.
Several weeks later, Julia is back home in Paris and on bed rest, awaiting the birth of her child. All in one day Julia learns that Mamé has had a stroke and that Bertrand is again having an affair with Amélie. As she is about to leave for the hospital to see Mamé, William shows up at Julia’s door, finally ready to learn about his mother. The two of them go to the hospital together, where William meets Edouard. Julia translates Sarah’s diary, which William has discovered along with the cupboard key. William also reveals that Sarah’s death was a suicide. At home that evening, the Tézac family and Julia receive another shock when Zoë announces that Mamé knew all along about Sarah, despite her husband and son’s efforts to keep Sarah a secret.
Three years later, Julia has separated from Bertrand and is living in New York City with Zoë and her new baby daughter. Incredibly unhappy, Julia thinks often about looking up William. One day she receives an out-of-the-blue call from William, who also now finds himself divorced and living in New York City. The two agree to meet for coffee, where they discuss Sarah Starzynski and where Julia reveals that she has named her new daughter Sarah in honor of William’s mother. Julia and William clasp hands and cry together.