The TSG summary is pretty fair.   This is a Victorian London-set fantasy Sherlock retelling, including BBC version vibes, but also the diverse power of Addison's imagination.  I personally found it a bit of a mixed bag.  I loved the relationship of angels to public buildings, and could have read a LOT more about that aspect.  Sherlock and Doyle's friendship develops beautifully over the book, and is everything I could have wanted.  However, the story is structured as canon-based short stories, with an overarching Jack the Ripper plot.  I found the individual tales a little too close to the originals to be as exciting as I wanted them to be, and I am so very done with that particular serial killer too.

Recommended to people who loved BBC Sherlock, and can imagine him as a Victorian-set angel -- but perhaps haven't read A. C. Doyle's original stories, so this will be both novel and familiar.  Not really a spoiler, but something the author only mentions at the end,

this started life as a Sherlock wingfic, which I am delighted by, because I thought that tiny subgenre of fanfic had died out years ago.  And yes, Cumberbatch's swishy coat can indeed pass for a pair of wings with a little imagination.