"The eldest was a razor-sharp novelist of upper-class manners; the second was loved by John Betjeman; the third was a fascist who married Oswald Mosley; the fourth idolized Hitler and shot herself in the head when Britain declared war on Germany; the fifth was a member of the American Communist Party; the sixth became Duchess of Devonshire. They were the Mitford sisters: Nancy, Pamela, Diana, Unity, Jessica, and Deborah. Born into country-house privilege...