Books like Secret Rooms by Catherine Bailey

Cotton Malone, a retired Justice Department operative turned antiquarian bookseller, is drawn back into a perilous treasure hunt for the lost riches of the Knights Templar, pursuing a rival of assassins and uncovering a conspiracy that could alter the modern world.

Lady Almina and the Real Downton Abbey tells the story behind Highclere Castle, the real-life inspiration for the hit PBS show Downton Abbey, and the life of one of its most famous inhabitants, Lady Almina, the 5th Countess of Carnarvon and the basis of the fictional character Lady Cora Crawley. Drawing on a rich store of materials from the archives of Highclere Castle, including diaries, letters, and photographs, the current Lady Carnarvon has written a transporting story of this fabled home on the brink of war. Much like her Masterpiece Classic counterpart, Lady Almina was the daughter of a wealthy industrialist, Alfred de Rothschild, who married his daughter off at a young age, her dowry serving as the crucial link in the effort to preserve the Earl of Carnarvon's ancestral home. Throwing open the doors of Highclere Castle to tend to the wounded of World War I, Lady Almina distinguished herself as a brave and remarkable woman. This rich tale contrasts the splendor of Edwardian life in a great house against the backdrop of the First World War and offers an inspiring and revealing picture of the woman at the center of the history of Highclere Castle. - Publisher.

A first‑person mystery where a former lover’s husband is found dead at midnight, and the ex‑wife stands over the body with a gun. The narrator hunts clues to uncover the unexpected murderer.

Sample pages Google Books for the 1998 reprint edition https://books.google.com/books?id=2ky-BAAAQBAJ&printsec=frontcover