"Wouldn't it be dread," wrote the Duchess of Devonshire, "if one had (a) no sisters (b) sisters who didn't write." As it was, the former Deborah Mitford had five scribbling siblings—including Jessica (The American Way of Death) and Nancy (Love in a Cold Climate)—who went everywhere, knew everyone (Churchills, Kennedys, Rothschilds, Sitwells, the royals...), and didn't let a day go by without keeping one another posted. Over 600 of their letters—funny, loving, sparkly, snarky, heartbreaking, chilling, gossipy, wise—have been collected by Charlotte Mosley (Diana's daughter-in-law) in The Mitfords: Letters Between Six Sisters. Keep an eye on the footnotes and a thumb in the index of nicknames (everyone had at least five), and you'll be rewarded with six up-close, personal—and sometimes appalling—takes on the 20th century. Here's Unity, the Hitler groupie, in 1935: "The Führer was heavenly, in his best mood, and very gay... He talked a lot about Jews, which was lovely."