Do you remember this show "Father Dowling Mysteries" or "Father Dowling Investigates" in UK (or "Detektyw w sutannie" for all my Polish comrades)?
This book is like this show, only in 19th century Russia. There is a fatherly, protective provincial bishop Reverend Mitrofanii and there is witty, a little-to-pretty-to-be-a-nun Sister Pelagia. And there are some dead people, dead dogs, sex scandals and what not.
Boris Akunin stays true to the tradition of the Russian novel and starts the book off with lengthy introductions of various characters that might or might not reappear in the book and he includes all their names, nicknames, surnames and patronymics. I really don't have the brain power to process all that. I prefer when the characterization is short and to the point like when Akunin describes Anton Antonovich von Haggenau who "used to be a German, but he completely recovered."
Strangely enough, the only character about whom we know very little is Sister Pelagia. We don't know why she ended up as a nun (it is clear it hasn't always been her calling) or why Mitrofanii singled her out. I suppose it will all be revealed slowly in following books.
The mystery itself revolves around some white bulldogs that drop dead one after another and Synodical Inspector who arrives from St Petersburg like the Spanish Inquisition bent on eradicating everything that is not Russian Orthodox Church, be it the Old Believers or even "older" believers, i.e. pure pagans.
Akunin is a true master of leaving the clues for you all over the book without making anything too obvious. He is not one of those rubbish crime writers, who will withhold an important piece of information revealed to the detective in the story but not to the reader. No, Akunin gives you all, whether you can piece together before Sister Pelagia is an entirely different matter.
If you like well-crafted intrigues, try Akunin. I thought "Pelagia and the White Bulldog" was amazing and apparently that is his 'weaker' series.