The Vanishing Man by Charles Finch

Charles Lenox is a nobleman who is working in a very unusual profession for someone of his status - that of a private detective. London in the mid-1800s is clearly divided by class into the aristocracy and lower working classes and they do not do business together. Lenox with the help of his best friend who just happens to be the love of his life and happily married solves the case of a theft, murder, and treasure that has been kept a secret for generations. Somehow they manage to do so amidst the parties and social gatherings one must attend as nobility. I love the relationship between Charles and Lady Jane Grey as well as the antics between Charles and his 12-year-old precocious visitor Lancelot. Witty, stylish and so true to character, this is a who-done-it with sophistication and fun. This is a prequel to the series but can easily be read as a standalone.