Among the six daughters and one son born to David, second Lord Redesdale, and his wife Sydney, were Nancy, the novelist and historian; Diana, who married fascist leader Sir Oswald Mosley; Unity, friend of Hitler; Jessica, who became a communist and investigative journalist; and Deborah, Duchess of Devonshire and mistress of Chatsworth. The Mitford girls, as John Betjeman called them, were one of this century's most controversial families; said to be always either in shrieks of laughter or floods of tears, they were glamorous, romantic, and - especially in politics - extreme. Yet the teasing, often bordering on cruelty, the flamboyant contrasts and the violent disagreements hid a powerful affection, subtle likenesses in character, and a powerful underlying unity...