Felix is a ten-year-old Jewish boy residing in a Polish orphanage in 1942. His parents, who formerly operated a bookshop, left him there for protection prior to the story's start. He wears glasses, possesses a vivid imagination, and relies on storytelling to make sense of the wartime world. He carries a yellow notebook filled with original fiction and letters from his parents.

Zelda is a precocious six-year-old girl who joins Felix on his journey through the countryside. She displays a limited understanding of the dangerous events unfolding around her, relying heavily on Felix's stories for comfort. She wears a locket containing pictures of her parents.

Barney is a large, bearded Jewish dentist living in a Polish ghetto. He frequently wears a leather jacket with a bullet hole in the back and carries a large medical bag. He uses his dental profession to curry favor with the authorities while secretly sheltering children in a cellar beneath a defunct print shop.

Mother Minka is the severe yet caring head Catholic nun at the mountain orphanage where Felix resides. As a former customer of Felix's parents, she agreed to hide him despite the severe risk harboring a Jewish child poses to her institution. She attempts to shield Felix from the reality of the outside world.

Dodie is a young boy living at the mountain orphanage and one of Felix's closest companions. He fears the older bullies at the facility and worries about the newly arrived children.

Jankiel is a recently arrived child at the mountain orphanage. He knows the grim reality of the outside world but swore an oath of secrecy to the nuns to maintain the ignorance of the other children.

Sister Elwira is the cook at the mountain orphanage. She sneaks a whole carrot into Felix's thin, watery cabbage soup as a gesture of sympathy for his situation.

Wiktor is a former schoolmate of Felix whose family moves into Felix's old home. He acts aggressively toward Felix and chases him away from the property when Felix arrives looking for his parents.

Mr. Kopek is a man from Felix's home village. Despite the grave danger involved in aiding a Jewish child, he provides Felix with bread and water while warning him about the forced removal of the village's Jewish population.

Henryk is a five-year-old boy sheltered in the underground cellar. He frequently cries for his home and parents, prompting the older inhabitants to comfort him.

Ruth is a curly-haired young girl sheltering with the other youths in Barney's underground hiding place. She listens to the stories the older children tell.

Jacob is one of the young boys hidden in the print shop cellar. He discovers a method to stack the beds so the children can peek out the high window at the passing feet on the street level.

Chaya is an older girl residing in the cellar beneath the defunct print shop, hiding under Barney's care.