To most Americans, Roald Dahl is a children’s book author — the imaginative, intimidating, and somewhat insane mind behind beloved books like Matilda, Charlie and the Chocolate Factory, James and the Giant Peach, and The BFG. Those who know his work a little better might be aware of his adult short fiction, some of which was adapted for the 1960s anthology show Alfred Hitchcock Presents — or even his R-rated adult work like Switch, Bitch and My Uncle Oswald, which deal with themes of colonialism and sexual violence. Then there’s his biography — he was a fighter pilot for England,...