Enola Holmes and the Cryptic Crinoline by Nancy Springer: I like Enola Holmes. She's spunky, resourceful, and bright. While her life would be much easier if she would just trust her brother Sherlock, it's understandable why she doesn't, and chooses instead to rely on her own instincts and deductive reasoning skills. In this, the fifth in the series, Enola's landlady, Mrs. Tupper, goes missing. Enola unravels the mystery, which leads to Mrs. Tupper's past during the Crimean War and to a meeting with Florence Nightingale. The historical setting is believable, Enola's cat-and-mouse game with her brother balanced nicely against the central mystery, and the mystery and codes compelling. A really fun series. The first is Enola Holmes and the Case of the Missing Marquess.
Source disclosure: I purchased this book.