[I received a copy of this novel through NetGalley.]
First, please note this is not a standalone novel, contrary to what I thought when I requested it, but part of a series (and very likely the last volume). However, I didn't find it difficult to follow the story and understand the characters: when the narrator alludes to events of the past or people he had previously met, he always adds a couple of sentences, nothing too long, just enough for a reader to understand the context. So this was good with me.
The setting here is that of feudal Japan (the Emperor and his court, bushi, military governors, geisha and courtesans) with a dash of supernatural: ghosts and youkai are common knowledge, and onmyôji and priestesses have actual power. In this world, Yamada and his faithful friend Kenji are confronted to attempted murder and political intrigue, from the Ise temple to the capital and the Emperor's court; I found the mystery decent enough, not too complicated (my guesses about a few things turned out to be right) yet not too easy either for the characters to understand, without convenient deus ex machina bringing the answers (Yamada deducted those).
It took me a couple of weeks to read, but it definitely wasn't boring (that was much more a matter of having lots of things to do and needing to prioritise other books in the meantime). The events made sense, the characters were likeable, and even though it's not my favourite novel ever, it was entertaining and believable.
On the downside, there were instances of Yamada 'hiding' things from the reader, which I don't particularly appreciate in mystery novels, and the female characters, while attaching, didn't have much to do apart from conveniently be here when a specific piece of information was needed, or wait in their palace for the men to do all the work. Granted, the setting itself doesn't lend itself to a lot of female freedom (aristocratic constraints, expectations placed on princesses, and so on), but it didn't help.
Conclusion: Still enjoyable in spite of these flaws.