What a perniciously pleasant surprise, The Mephisto Club, by Tess Gerritsen!
The Mephisto Club, sixth in the Jane Rizzoli detective series (though my virgin Rizzoli read) incorporates several favorite interests of mine: mysterious, though not-at-all-like-The-Da-Vinci-Code, secret societies, apocryphal literature (i.e., The Book of Enoch and The Book of Jubilees), symbiology and, dare I admit it (please don't strike me down dead Lawd, please!) demon ... uh ... ology. As in, "The sow is mine!"
Now, I'm no aspiring warlock or wiccan, and The Mephisto Club would probably bore a fun loving Aleister Crowley occultist (might as well try interesting a Navy Seal in an exciting game of Battleship™), but for a Luciferian lightweight like me possessing (don't pardon the fun pun) merely an arguably unhealthy interest in stories satanic, The Mephisto Club, with its ritualistic skin carvings, filleting, dastardly dismemberments, demon and devil huntings, priestly affairs (Vatican ordained and carnal), and claustrophobic chases through the narrow cobblestone lanes of the dank back alleys of Rome, beautifully rendered in above-average, often accomplished prose, fit the fun, page-turning, Beelzebubbish bill for me just fine. Very fine.