What is the author's tone in the novel, The Librarian of Auschwitz?

When simplified, Iturbe is telling the story of concentration camps during the Second World War, and therefore the tone is inherently negative. However, Dita's innocence allows her to hold on to some of the optimism that the older prisoners have lost. Naturally, the events in the story have a depressing tone, the emotional and graphic imagery is heartbreaking and vile.