The Janissary Tree, by Jason Goodwin (novel). Great concept – detective novel set in 19th century Ottoman Istanbul/Constantinople. Somewhat patchy execution; the resolution of the central mystery is contrived even by the standards of the genre. I think it works best as a love letter to a vanished world.
Catherine the Great: Portrait of a Woman, by Robert Massie (non-fiction). Now this is more like it. The first few chapters bring the young Catherine and her world alive; I look forward to consuming more! Worth a look for Empire: Total War and EU4 fans.
Lest Darkness Fall, by L Sprague de Camp (novel – the first Amazon link goes to my paperback edition. There also looks to be a newer Kindle omnibus). A time traveller journeys back to Ostrogothic Rome, on the eve of the Dark Ages. Luckily, he just happens to have the historical knowledge to turn the tide. I’ve enjoyed this alternate history romp since I was a teen; it’s clever, funny, and the characters are a blast. Clearly, the author was having the time of his life! Here is a more detailed writeup.