After the Ninth Duke of Rutland, one of the wealthiest men in Britain, died alone in a cramped room in the servants' quarters of Belvoir Castle on April 21, 1940, his son and heir ordered the room, which contained the Rutland family archives, sealed. Sixty years later, Catherine Bailey became the first historian given access. What she discovered was a mystery. The Duke had painstakingly erased three periods of his life from all family records. But...