A little boy running from the people who killed his mother, brother and sister is lost for months in a dark forest in Eastern Europe. He survives on wild berries and ties himself to trees to escape the howling wolves. Frozen and starving, he happens upon a hut that holds out the promise of food and warmth, but as with the hut in “Hansel and Gretel,” the promise is cruelly deceptive, and again he narrowly escapes death. Eventually he is rescued by soldiers. But they are dangerous, too, and he must hide from them the truth about himself. It is a truth so frightening that as time passes he gradually forgets who he is, to the point that he cannot even remember his name.

It could be a fairy tale from the Brothers Grimm. But “The Mascot: Unraveling the Mystery of My Jewish Father’s Nazi Boyhood,” by the Australian writer Mark Kurzem, is a true story. Part mystery, part memory puzzle, it is written in the polished style of a good thriller, and it is spellbinding....

It is an anguished tale set in the morally gray zone between culpability and survival. The soldier discovered that the boy was Jewish — he was circumcised — and warned him to hide it. The others thought he was Russian and named him Uldis Kurzemnieks. They made him their mascot, a miniature soldier with a uniform decorated with Nazi insignia. As he traveled with them, he said, he witnessed atrocities, including hundreds of Jews being herded into a synagogue and burned alive. He became a propaganda tool, the Reich’s youngest Nazi, the subject of newspaper articles and a documentary.