In the late 20th century, Hannah Stern is a 12-year-old Jewish girl headed from her home in New Rochelle, New York, to visit her relatives in the Bronx for a Passover Seder. Hannah views her family’s Jewish traditions as a boring obligation, and she is afraid of her Grandpa Will, who has fits where he seems to be back in the past. He also has a tattoo from his time in a concentration camp. But everything changes for Hannah when, in the middle of the Seder, she opens the door of the apartment and walks through it to a Polish shtetl in 1942, right in the middle of World War II and the Holocaust.
In the past, everyone believes that Hannah is Chaya, a girl whose parents recently died of disease back when she lived in Lublin. Shmuel and Gitl are siblings who have taken Chaya (now Hannah) in to raise her as their own child. Shmuel is about to marry his true love, a local woman named Fayge, but Gitl has rejected all marriage advances, including those from a local butcher named Yitzchak.
Shmuel and Fayge’s wedding festivities are suddenly interrupted when a group of Nazis comes to the shtetl and orders all of the Jewish people there to board some trucks so that they can go be “resettled” at a concentration camp. Hannah tries to warn everyone about the Holocaust, but they dismiss her, believing she is still delirious and confused after her recent illness in Lublin.
The journey by truck and train to the concentration camp is brutal, with many people—including Hannah’s new friend Rachel—dying along the way. When Hannah finally makes it to the concentration camp, she learns that the Nazis are forcing the Jewish people to perform hard labor for them.
It takes Hannah a few days to get used to life in the concentration camp. During that time, one of her most important allies is Rivka, a girl who is younger than Hannah but who knows all about concentration camp life. Rivka learned various tricks to survive the hard way, after almost every member of her family died. Hannah and the other members of her shtetl learn that the true purpose of the concentration camp isn’t work but death, with the most vulnerable Jewish people who can’t work anymore being marked for death and burned up in furnaces connected to big chimneys.
Rivka teaches Hannah that the best way to avoid being chosen for death is to follow the rules and avoid attracting attention. In particular, Hannah tries to avoid the camp commandant and a fellow non-Jewish prisoner called the blokova, who is missing two fingers and who cruelly rules over the other prisoners. But no matter what Hannah does, she continues to witness death around her, with Yitzchak’s young children Tzipporah and Reuven both dying in the camp.
His children’s deaths motivate Yitzchak to start forming an escape plan for himself, Shmuel, Gitl, and eventually Hannah. But when the plan goes wrong, Gitl and Hannah barely manage to make it back to their barracks without getting caught. Yitzchak manages to escape, but a firing squad kills Shmuel, and Fayge joins him and dies, too.
One day, a new guard approaches Hannah, Rivka, and two of their friends, and he accuses them of not working. He is responsible for choosing people to die and says he has to fill three more spaces. Although Hannah initially avoids being picked, she decides to secretly change places with Rivka. She figures that Rivka only has one life to live, but Hannah still has her other life back in present-day America. Hannah tells her two friends about her future life in America as they all go to their presumed death in a dark room under the chimneys, which they call the Cave of Lilith.
But just as Hannah’s eyes adjust to the darkness in the Cave of Lilith, she realizes that she is back in her grandparents’ apartment at the Seder. With a much better understanding of Jewish history, Hannah realizes that her favorite older relative, Aunt Eva, is in fact her friend Rivka, since they have the same identification number tattoo from the concentration camp. After her experience in the past, Hannah now better understands what it means to be Jewish.
Later, Aunt Eva tells Hannah about the few concentration camp prisoners who survived and how, after the war, both Gitl and Yitzchak moved to the new country of Israel, where they lived to old age and had fulfilling lives.
