My grandmother’s childhood in Weimar Germany was, at least as she described it, idyllic. She grew up in Grunewald, a leafy section of Berlin, swimming and boating in the district’s many lovely lakes. Her parents, though Jewish, threw elaborate Christmas parties and hosted birthday celebrations at which their three daughters were expected to recite poetry. They sent the girls to summer camp and private school and considered themselves assimilated into the city’s haute bourgeoisie. Even after the Reichstag fire, which occurred when my grandmother was twenty, there was, she insisted, still plenty of fun to be had. She liked to...