Listed in publication order. 

From Goodreads: Charles Lenox, Victorian gentleman and armchair explorer, likes nothing more than to relax in his private study with a cup of tea, a roaring fire and a good book. But he can’t pass up a good mystery, and this amateur sleuth is often called on to leave his comforts behind in the pursuit of clues. Follow him into the public houses, Mayfair mansions and servants’ quarters of Victorian London, into the intrigues of Parliament and secrets of Oxford. This historical mystery series, with its keen eye for period detail and razor-sharp plotting, offers readers an unparalleled brand of charm, sophistication and suspense.