One of the earliest photographs of J Edgar Hoover shows him aged 17, standing tall and proud in the starched uniform of a high school cadet. At first glance he is a figure of innocence: a Hoover without victims. But the fact he wore such a uniform to teach Sunday school classes is indicative of a young man on a divine mission. “Sunday school was boot camp, the training ground in the battle for the soul of the nation, and Hoover dressed the part,” writes Lerone Martin, academic and author. “It was 1912, and J Edgar Hoover was his own...