The Art of Detection is the last of Laurie R. King's Kate Martinelli books, and thank goodness. I really don't think I could have handled another one, but King is a compelling enough writer that her books are hard to put down.
The easily noticed theme of The Art of Detection is "my research, let me show you it." The body of a Sherlock Holmes enthusiast (to the extent that a significant portion of his home is a Baker Street replica) is found in the old defense complex in the Marin headlands. This affords King the opportunity to show off both her Holmes-era research (I would probably find this less annoying if I didn't know her other series is Holmes fan fic) and her Marin Headlands research. The Holmes research allows her to get all the details of the enthusiast's home right. The Headlands research is just paragraphs of exposition you can skip.
The real theme of the book, it turns out, is marriage equality, but in an annoying way. I started to suspect that might be what the book is about at the first mention of the mayor. There was something about the way King referred to him that made me guess it was going to be Newsom. The murder mystery hinges on a possibly authentic lost Holmes manuscript, which turns out to be the tale of a soldier who loved and wanted to marry a crossdressing performer - and went so far as to write to a lawyer and ask, essentially, if he could get away with it if his partner continued to live as a woman. And then there's the end. Roz and Maj tell Kate and Lee to avoid the news and anyone who might want to pass it on to them. Then they show up the next morning and whisk their family off to City Hall so the two couples can be some of the first couples getting married. It felt a lot like Newsom started granting marriage licenses and King thought, "Oh, good, now they can get married so I can write another book about them," and then wove the whole story around that while throwing in her Holmes knowledge so she didn't have to research something new. Why do all mainstream queer stories have to be issue fic? That's the exact opposite of what I was looking for by reading this series.
The other problem with the book is that King has written and included the entire supposed Holmes manuscript. When I got to the first part of it, I despaired at the thought of having to read it all. But it turns out that the Holmes story is much more engaging than Kate's mystery. I expect that this is because King didn't really know what to do with Kate at this point. Part of that may be how much Kate's circumstances have changed: this book moves us forward several years from the last book. Kate and Lee have a daughter and have moved from their Russian Hill home to a place that has more of a neighborhood feel. Their friend Jon is partnered to the guy he was dating in the last book and they also have a kid. Perhaps the best part of the shift in time is what has happened with Roz and Maj. At this point, Kate and Lee are just beginning to be close to them again, and Roz is hanging back from getting into elected politics herself. I liked that there were consequences for their actions in the last book.