On the way back to Himmel street the burning book becomes too painful and Liesel has to take it out from under her uniform. Hans is shocked to see it, but he promises not to tell Rosa if Liesel will keep this book, and anything else Hans requests, a secret. Liesel thinks he is only mad at her stealing, but Hans is thinking about the consequences of such actions with the Nazis.
Hans reinforces the idea of keeping a secret private life separate from her public persona. Liesel does not yet grasp the political consequences of her actions – she is still thinking of parental punishment, but Hans sees how the worlds overlap, and that Liesel's books could be dangerous for her and for them.
A few days later Hans trades some cigarettes for a copy of Mein Kampf, the book written by Hitler. He overhears the party members discussing him, and how he will never be allowed to join the Nazis. Hans feels pleased with his plan, which will unfold later, and involves using Mein Kampf as a sort of shield.
Hans gets his idea from both his son and Liesel. This physical copy of Hitler's book will become an important symbol later, but for now it represents a foil to those books so precious to Liesel.