Caging Skies by Christine Leunens as compared to the movie adaptation, JoJo Rabbit

An avid member of the Hitler Youth in 1940s Vienna, Johannes Betzler, discovers his parents are hiding a Jewish girl named Elsa behind a false wall in their home. His initial horror turns to interest—then love and obsession. After his parents disappear, Johannes is the only one aware of Elsa’s existence in the house and the only one responsible for her survival.