It is the year 1942 in Paris, France. The scene opens with a young girl playing with her brother in a bedroom. The two children are laughing and having fun together when several sharp knocks sound on the front door of the apartment. The girl, Sarah Starzynski (Mélusine Mayance) immediately quiets down. Sarah and her mother, Madame Starzynski (Natasha Mashkevich), go to the front door and and are greeted by two French policemen. They are able to see Sarah and her mother, but they do not see or hear her brother or her father. Sarah says that both her father and her brother have been missing for several days, but inside she knows that her brother is in the bedroom.Sarah rushes back to the bedroom where her brother is and tells him to hide in a closet, despite his protests. The boy reluctantly climbs in after Sarah tells him that it is just like the game that they played before, and that she will be back soon. Sarah locks the door, then takes the key, holding it tightly in her hand. Sarah and her mother are then arrested by the officers. On their way out of the alleyway, they bump into Sarah's father, M. Starzynski (Arben Bajraktaraj, and the officers arrest him as well.Sarah's family, except for her brother, are all loaded into trucks to be taken to the Velodrome d'Hiver, where many other arrested Jews are also kept in unsanitary, dim and generally inhuman conditions by the Paris police force and the French Secret Service. While there, Sarah's family meets another woman. The family and the woman are having a conversation about what is happening when the woman pricks her gums, starts violently coughing so she can attempt to find a way out. Mme. Starzynski, panicked, calls for a doctor. The woman reports that she is coughing blood up. A nurse takes her away to the infirmary. From their vantage point, Sarah and her family are able to see the woman enter the infirmary, come out with several papers, then leave the Velodrome after presenting said papers to the guards. M. Starzynski, stunned, yells at the guards to stop her so he could give her the closet key. The guards refuse, and instead slam a gun butt in his head, dazing him. He is then told to stand up and go back to the area in the Velodrome where he came from.The deportees are then transferred to the French Beaune-la-Rolande containment camp. This was not a concentration camp, and the purpose was not to force labor or to kill the inmates. There is strict order that men are to go to one side, and that women and children are to go to other side. M. Starzynski is separated from his family. He says that he will see them soon. He is never seen again.Later, the women and the children are split from each other. There is much reluctance to do so, and many mothers protest, holding on to their children, and their children doing the same. Mme. Starzynski and Sarah are separated, but when Mme. Starzynski attempts to run and get Sarah, complete pandemonium ensues. The French guards are unable to restore order without resorting to physical force. The guards use their guns to hit the inmates to separate them. When Mme. Starzynski finds Sarah, the two sit on the ground, hoping. Suddenly, a French guard uses a powerful stream of water to separate them.Later in the day, there is commotion as the children crowd around a portion of barbed wire. The women of the camp are trying to hand the children fruits and bread, much to the guards amusement. Sarah notices an apple fall from a woman's hand to the ground. As she reaches for the apple, one of the guards steps on the apple to prevent Sarah from getting at it. Sarah looks at the guard sympathetically, and he releases his foot from the apple, allowing Sarah to take it. This is the last time that the women will ever be seen.The children are now on their own in the camp. Sarah comes down with a fever, and she falls asleep for three days. She awakens to another girl sitting on her bunk in the barrack, who informs her that she has been sick for a while. Sarah suddenly remembers the key, but she cannot find it. As she is looking, the other girl pulls out the key from her pocket and asks Sarah if she is looking for it. Sarah grabs the key as the other girl introduces herself as Rachel (Sarah Ber). Sarah secretively explains to Rachel that she locked her brother in a closet to avoid having the French police find him, and that she must get back to Paris to let him out. The two girls agree to go with each other, and escape. They sit in the barrack, contemplating the best way to do it.The two girls eventually decide to escape during the day. They figure that when the sun is out, it will be hot and the guards will be in the shade. Sarah remembers seeing a small ditch under a portion of barbed wire. If they were to escape at night, the guards would notice any movement, and they have searchlights. Sarah tells Rachel to layer up with as many sweaters as she can. When Rachel questions this logic, Sarah explains that the barbed wire around the camp will hurt less when they crawl under it.The two girls hatch their plan, sneaking out of the barracks in broad daylight. It is sweltering hot outside. Like they expected, all of the guards are in the shade, and are avoiding looking in the sun. The two girls run over to the barbed wire, in their sweaters. Sarah finds the ditch, and lifts the barbed wire over it so that Rachel can escape. When Rachel is about halfway through the wire, a large shadow appears, from the guard. Both of the girls look up at him. The guard announces that escaping is against the rules. Sarah looks at the guard and quietly says his name, Jacques. The officer, stunned, asks how Sarah knows his name. Sarah remembers when the officer released the apple for her, and shortly after, heard someone say his name. She is able to break the officer by saying that she will never forget him for what he has done. The officer, emotional, looks around, then lifts up the wire for the two girls to escape.The two girls run through a field of grain, then into a forest. Rachel realizes that if they are to have any chance of not getting caught, they need to remove their yellow stars, indicating that they are Jews. As night falls, the two girls look desperately for any sign of civilization. Rachel, however, is getting weak, and is not sure if she will be able to make it back to Paris. Suddenly, Sarah sees lights coming from a village, and begins running towards it. They are roaming the streets, when they see a series of military trucks. The girls rush to hide. After that, they begin roaming the streets, looking for anyone that can help them. They come across a house with the windows open. Sarah shouts, trying to gain their attention so that they can help Rachel. The man inside shuns both of the girls and slam the windows shut. The girls find the mans shed and sleep for the night.The next morning, the man comes to the shed to find the two girls sleeping. He shouts at them to scram, but Sarah explains that her friend is gravely ill. The man, hesitating, looks around and takes both of the girls to the home. Sarah introduces herself under a fake name, but Rachel is too ill to speak. The owner of the home, Jules Dufaure (Niels Arestrup) and his wife, Genevieve Dufaure (Dominique Frot), decide to call a physician to examine the girl. The physician arrives with a German officer. While the physician treats Rachel, the guard asks if there is another child, since there was recently an escape at the camp. Genevieve, knowing this might happen, had hid Sarah before the officer came. Genevieve and Jules both agree to let the officer inspect the home. As the officer begins his search, the doctor comes back, announcing that Rachel has died. The officer, distracted, follows the physician back outside. The two men leave, leaving Genevieve, Jules and Sarah in the home.Days later, the Dufaures board a train to take Sarah back to her family's apartment in Paris. The Dufaures, not wanting trouble for having one of the escapees, dress Sarah in boy's clothes to avoid detection, and Jules creates fake identification papers for Sarah. When an officer comes around to check the papers, Jules papers are copied well enough to fool the officer, and Sarah is allowed to continue. In Paris, Sarah rushes into the apartment building, and despite the Dufaures calls for her to be cautious, Sarah keeps running. She runs up to the third floor, knocking furiously on the apartment door. A young boy opens the door and answers; Sarah pushes him aside without explanation and finds the closet where she locked her brother. When she unlocks the cupboard, she is horrified by what she finds, and screams hysterically. The audience presumes that the boy has died.After the war, Sarah continues to live as a family member with the Dufaures and their two grandsons. When she turns 18, she moves to the United States, hoping to put everything that happened behind her. She stops corresponding with the Dufaures when she gets married and has a son, William. When her son is nine, Sarah still despondent and blaming herself for her brother's death commits suicide by driving her car into the path of an oncoming truck. It's explained to her son that her death was an accident.The movie cuts to the present day, 2009. A magazine journalist, Julia (Kristin Scott Thomas) has inherited the French apartment of her grandparents. Julia does not know this, but her great-grandfather was the boy who opened the door to Sarah in 1942. Julia, having done an article on the French roundup of Jews, finds herself craving more about the history of the apartment, especially since she learns that the apartment came into her husband's family at about the time of the French roundup, and she begins to investigate the people involved in the ownership of that apartment unit.Julia begins an obsessive quest to find any trace of Sarah, eventually learning of her life in Brooklyn and finally locating William Rainsford (Aidan Quinn) in Italy, after extensive reasoning revealed that his grandmother was in fact Sarah Starzynski. She meets with him in Florence, Italy, and asks him for information about his mother, but learns to her surprise that William does not know his mother's history or even that she was a Jew, believing only that she had been a French farm girl. Listening in amazement, William rejects the story and dismisses Julia. Later, everything is confirmed to William by his dying father, Richard, including Sarah's suicide. He gives William Sarah's journals and notes, telling him Sarah immediately had William baptized right after his birth, fearing that "being Jewish" was a threat to him and explaining that "...we're all a product of our history." The key to the cupboard is among the items handed to him by his father.Julia, having given up hope of having another child after years of unsuccessful attempts to conceive with her ex-husband, Bertrand Tezac (Frédéric Pierrot), discovers she's pregnant. Her husband loves their life with their 12-year-old daughter, Zoe, as it is and does not want to have another child at this point in life. Julia ultimately decides against an abortion, has another daughter, divorces her husband and eventually moves with her new baby daughter to New York City.Two years later, William, having contacted Julia, meets her for a late lunch in a restaurant favored by Sarah and gives her additional information about his mother that the Dufaures had. Julia is amazed and happy for him, and has brought her young daughter along to the meeting. William breaks into tears when Julia tells him her daughter's name is Sarah. Julia comforts him as they both look at little Sarah.