once by morris gleitzman

The year is 1942. Felix is the son of Jewish parents who run a bookshop in Poland, after his parents could no longer afford to keep him. They said they would come back for him at the orphanage when they had got over their financial problems. When the Nazis destroy the small library in the orphanage, Felix uses this opportunity to escape and search for his parents. Leaving the orphanage behind, Felix as a lone Jewish boy searching around Poland for his parent. Not for long, he befriends Zelda, a little girl whose parents have been shot. Together they meet Barney, a dentist who is protecting a group of children in a Jewish ghetto. It was not for long until they all got caught and was sent to the Nazis death camp by train. One of the boys was able to knock down the door on the speeding train and this could be their only chance to escape the death camp. But will Felix and his friend have enough courage to make it out alive?