In her history of England's Mitford sisters, who were major figures in the international political, literary and social scenes for much of the 20th century, Lovell (The Sound of Wings: The Biography of Amelia Earhart; etc.) rises with aplomb to the challenges of a group biography, deftly weaving together the narrative threads of six at times radically disparate lives to create a fascinating account of a fascinating family. Born into the ranks of the minor aristocracy and educated at home by eccentric and perennially cash-strapped parents, Nancy, Pamela, Diana, Unity, Jessica and Deborah Mitford hardly seemed the types whose exploits would generate endless fodder for the sensationalist press. But when Diana left her wealthy young husband to take up with and eventually marry Sir Oswald Mosley, infamous leader of British fascism; when Unity became close friends with Adolf Hitler and a proponent of Nazism; when Jessica, a vocal Communist, eloped with a notorious cousin who was also a nephew of Winston Churchill; when Deborah married the Duke of Devonshire; and when both Nancy (Love in a Cold Climate) and Jessica (The American Way of Death) became acclaimed, bestselling authors, the world responded with avid, insatiable and at times alarmingly intrusive curiosity. But whether adored or reviled by their public, all the Mitford sisters were engaged with (and at times embodiments of) the major social and political issues of their time. Lovell's account of the sisters' upbringing and their often tumultuous adult lives is as lively and engrossing as Nancy's heavily autobiographical fiction; the group biography also does a commendable job of separating the myths that fiction created from the sometimes more mundane realities of the Mitfords' activities and relationships. 16 pages of photos not seen by PW. (Jan.)