The Secret Rooms by Catherine Bailey, 465 pages

When the 9th Duke of Rutland died alone in the cramped family archives on April 21, 1940, his son and heir, Charles, ordered the room sealed. Sixty years later, Catherine Bailey became one of the first historians allowed inside. What she discovered when she began reading through the duke's letters was a mystery involving one of the most powerful families in British society in the turbulent days leading up to World War I. The 9th Duke, who had devoted his entire adult life to organizing and cataloging several hundred years' worth of family correspondence, had carefully erased three periods of his life from the record. But why? Filled with fascinating real-life characters, a mysterious death, family secrets and affairs aplenty, The Secret Rooms is an enthralling, page-turning true story that reads like an Agatha Christie novel.