You need more than curiosity about Margaret to hold on and watch this royal mosaic take shape. For the first half, she co-stars at best as we follow ""Uncle David"" through his abdication and his marriage to Wallis Simpson. Then we look out of her father's eyes as Bertie suddenly finds himself King and later grows aware of his critical illness. Backgrounds crowd in--description of cabs and buses, historical precedents--even as Margaret grows from vivacious child to troublesome, dissatisfied adult. Her paradox: she despises playing second fiddle (while her sister is groomed for the throne), yet neither can she beat living constantly in the limelight--which locks her out of commoners' chances for fun and smothers much of her romantic life. Above all, Brough aspires to be fair: well-known but criticized actions by the principals are so securely framed as to appear natural, not matters for blame, and negative views of Margaret are expressed without comment as others' opinions. Glued to the end is a dive into the history of porphyria in the Royal Family--and the ability of that inherited condition to bring on insanity (as in George III) or, sometimes, irritability and migraines like Margaret's. Was the author learning something that would provide an excuse for Margaret? In any case, she is but a major theme in this portrait of monarchy's majestic hold on the British people, and its incipient end.