Katherine Addison. Released 23rd June 2020 by Macmillan on their Tor Forge imprint, it's 448 pages and available in hardcover, paperback, audio, and ebook formats. It's worth noting that the ebook format has a handy interactive table of contents as well as interactive links and references throughout. I've really become enamored of ebooks with interactive formats lately.
This is a wingfic retetelling of several Holmes and Watson adventures with Holmes reimagined as a black winged angel guarding over London, Dr. Doyle (Watson) battling a supernatural injury and the both of them solving mysteries and generally keeping London safer for the populace.
The author has a strong and deft touch with characterization and detailed flowing period dialogue. I felt, however, that the central characters weren't ever made to be anything but Holmes & Watson (with wings, yes, and Watson's trying not to turn into a soulless creature of the night... but other than that). I'm an admittedly huge canonical Holmes & Watson nerd, and the plots of the stories included are instantly recognizable and mostly unchanged.
There are some moderately subtle elements of gender fluidity and a sweet bromance between the titular characters in the book, but nothing graphic. In fact, the attraction(?) was too subtle for me. I wouldn't hold it up as a beacon of representation for LGBQTIA readers. It is straight up Holmes and Watson with supernatural creatures. The author is a very capable wordsmith and I did enjoy reading it very much, but the blurb promising "not the characters you expect" was a bit misleading because they were exactly the characters I expected. (and that, at least in my case, isn't a bad thing).
Disclosure: I received an ARC at no cost from the author/publisher for review purposes.