~~Note: This is a book reaction, not a full review.~~
Rather like Gail Carriger without all the werewolves, and with more of a Sherlock Holmes flavour. The opening scene is clearly an homage to "The Man with the Twisted Lip." Considering the characters keep uttering Emersonisms and Peabodyisms, I also suspect the book was strongly influenced by Elizabeth Peters' series. My biggest complaint--other than the way Quincannon's lecherous and possessive behaviour is treated as winsome rather than creepy as hell--is that their opinions and perspectives feel rather anachronistic. For example, the characters seem amazed that the wife of the opium fiend didn't leave her husband. While according to California law, women had recently gained the rights to any property they brought into a marriage, and simple infidelity was enough for a woman to obtain a divorce, separation and divorce were still outlandish, potentially scandalous, and exceedingly rare. (California was quite progressive--in the UK at this time, the infidelity had to be combined with cruelty, bestiality, bigamy, or incest.)
On the other hand, my skepticism over this and other scenes caused me to research and discover lovely little tidbits of history like the California divorce and property laws, so there is that.