The following version of the novel was used to create this study guide: Gleitzman, Morris. Once. Henry Holt and Co., March 30, 2010. Kindle.

In the historical novel Once by Morris Gleitzman (the first book in the Once series), Felix Salinger, a young Jewish boy has been left by his parents at a Polish orphanage. When Felix finds a whole carrot in his soup bowl, he believes it is a sign his parents are coming to get him. They left him more than three years before with the promise they would come back for him when their prospects as Jewish booksellers improved. They never told Felix about the Nazis’ hate for Jews or that they were leaving him at the orphanage to keep him safe.

Mother Minka, the nun in charge of the orphanage, sympathizes with Felix when he shares with her that he believed his parents were coming. She tells him the carrot was not a sign from his parents. Meanwhile, Felix sees Nazi soldiers burning books in the courtyard of the orphanage and has decided for himself that the Nazis are professional librarians who do not like Jewish books or Jewish booksellers.

Felix escapes the orphanage to look for his parents, believing that he can save them by warning them that the Nazis are looking for them. On his journey, he finds a Jewish home where it is clear the residents left in a hurry because their half-eaten food is still on the table. When Felix hears gunshots, he decides that the residents are probably off hunting rabbits. Later, Felix tries to hitch a ride with a group of soldiers in a truck. Felix believes that one soldier is trying to give Felix a thrill when he points his gun at Felix. The soldier’s gun fires as the truck hits a bump and a bullet whips past Felix's head. In his innocence, Felix believes the man unintentionally fired the gun and will later feel guilty about what happened.

After Felix locates the village where he lived with his parents and realizes that they are not there, Felix walks to the city, the place where he has been told his parents were taken. He begins to wonder why people hate him so much when he is run from his home by a Catholic family that claims that the house is now theirs. On his way to the city, Felix finds a little girl named Zelda, whose parents have been shot and their house set on fire. Felix takes Zelda, who had been knocked unconscious, with him. They are discovered by Nazi soldiers and are forced to walk to the city with a large group of Jews. During the walk, Felix comforts Zelda with stories and tries to shield her from the cruel ways the Nazis are treating the Jews.

In the city, a Nazi soldier tries to separate Zelda and Felix; but, a man wearing a Jewish armband holds up a bag in front of the Nazi soldier. He is allowed to take both Zelda and Felix. The man, named Barney, is hiding Jewish children in the basement of an abandoned printing press. In exchange, Barney, a dentist, does dental work for the Nazis. One day, Barney takes Felix with him when he has to fill a man’s tooth with no pain medication. He has Felix tell the man a story to distract him from the pain.

Nazi soldiers locate the place where Barney is caring for the Jewish children. They are taken to a train station. Although Felix does not know where the trains are taking the Jew, the reader can infer they are going to a concentration camp. Barney stays with the children to comfort and try to protect them. During the train trip, Felix and others discover there is a place where the wall of the car is rotten. They kick out the wall to make a hole big enough for a person to escape. Felix, Zelda, and another girl named Chaya are the only children brave enough to take their chances by jumping from the train. Felix and Zelda survive the jump, but Chaya dies. As Felix considers his future, he thinks about the syringes that Barney had with him on the train. Barney told him the syringes contained medicine that would put the children to sleep, permanently. Felix is comforted by knowing that Barney will use the medicine on the children instead of allowing them to be hurt.