I've read
this one before, being fond of Laurie R. King's Mary Russell series if not her Kate Martinelli one. (I have tried the latter, but couldn't care about the characters enough.) This is mostly a Martinelli novel with a Russell story inserted in the middle, quite cleverly, and I enjoy it very much despite my one-sided tastes.
Mind you, the Russell story isn't about Russell at all, it's about Holmes, but to a devotee of that series it doesn't matter; one can take it as an addendum to
Locked Rooms. Parallel murder mysteries and a clever look at the nature of "fiction". What is real, after all? Ms. King does love to play with the concept.
I recommend it, and frankly I think it can stand independent of either series, though a reader would get more from it after reading one or both series first.
Separately, I'd like to direct interested parties to
Open Library. It's a nifty idea and I hope it manages to take off.