Hannah Stern is a young Jewish girl living in New Rochelle, NY. She and her family, including her parents and younger brother Aaron, are to attend a Passover Seder at her grandparent's home. Hannah has no interest in attending. She is tired of hearing about the past and is uncomfortable listening to her Grandpa Will rant about his experiences in the concentration camp.
When Hannah rises from the table to symbolically open the door for the prophet Elijah, she is transported to Poland in 1942. There she inhabits the life of Chaya Abramowicz. She insists that her name is Hannah and that she lives in America but Chaya's aunt and uncle, Gitl and Shmuel, dismiss these claims as effects of Chaya's ordeal with cholera, from which she barely recovered. The disease claimed Chaya's parents and the adults assume Chaya is probably still grieving from this loss.
A man named Shmuel is to be married to Fayge, a woman in a neighboring village. On their way to the village they are stopped by Nazi soldiers who insist they must come with them to be relocated. Hannah is the only one who knows what is actually about to happen. She tries to explain why they must not go with the soldiers, but the adults explain that they have little choice. They are loaded onto trucks and driven off to a train station where they are herded into cattle cars with barely any room to breathe. The ride on the train lasts for days and several children and infants do not survive.
Hannah and the others finally arrive at the concentration camp where they are quickly divided by gender and age. The women and children remain together while the men live in separate barracks. The prisoners are showered and their hair is cut short. They are also tattooed with prisoner numbers. They are not fed until the next morning and then they only receive a watery potato soup and some bread as nourishment.
Hannah meets a young girl named Rivka who explains to her how to avoid being chosen for extermination. Rivka warns Hannah that when Commandant Breuer, the commanding Nazi officer, comes to the camp it is to identify those who are too weak to work so that they can be killed. If Hannah is to survive, Rivka says, she must learn quickly to do what she can to avoid being noticed. Rivka explains that most of her family has perished in the camp. Only her brother, Wolfe, remains.
The prisoners form their own system to help their chances. Items are stolen when possible as a form of mild protest and sometimes out of necessity. Gitl is able to learn what is going on in the men's camp through her forced labor position in the storage shed. She learns of a plan to escape.
Soon after, some of the men, including Shmuel Abramowicz, Chaya's uncle, attempt to escape from the camp. The escape attempt is thwarted but Yitzchak, a butcher from Chaya's village, is able to get away. The next morning those who were captured are executed in front of the others. Shmuel is among them. Fayge runs to be with him and they die together. Wolfe emerges from "Lilith's Cave", the name the prisoners have given to the doorway leading to the gas ovens. He carries Fayge's body away as part of his gruesome job.
One day, while fetching water for the kitchens, Hannah has a vision of girls in school uniforms playing around a fountain. She begins to discuss this vision with the other girls around her, but a new Nazi guard catches them talking instead of working. He tells them that he needs three more to be sent away (a euphemism for extermination). The guard chooses Rivka, Esther, and Shifre. Hannah is spared but decides to act to save Rivka's life. She takes Rivka's handkerchief from her head and places it on her own. She tells Rivka to run and hide until they are gone. Rivka goes without saying anything. Hannah then escorts Esther and Shifre as they are led to Lilith's Cave. She tells them that the Jewish people will endure this atrocity and have a country of their own one day. They will go to America as well and hold jobs as movie stars and politicians. The darkness of Lilith's Cave envelops Hannah and she finds herself alone in front of a door. She turns to look behind her and finds herself back in the dining room of her grandparent's home. Grandpa Will asks if the prophet Elijah is there or not. Hannah answers that no one is there and returns to her seat, her face pale from the experience.
At dinner Hannah notices the prisoner tattoo on Aunt Eva's arm and recognizes it. She explains the numerical relevance of the number to Aunt Eva, who confesses that when she was young she was known by another name: Rivka. After coming to America many of the survivors changed their names. Grandpa Will, Eva's brother, was known as Wolfe before. She tells Hannah that in addition to them, only Gitl and Yitzchak survived the camps. They both moved to Israel where Yitzchak became a politician. Gitl started a charity to help survivors of the Holocaust reunite with their families. She named the charity CHAYA, after her niece who perished in the camp.