The Mephisto Club

"PECCAVI"
The Latin word is scrawled in blood at the scene of a young woman's brutal murder: I HAVE SINNED. It's a chilling Christmas greeting for Boston medical examiner Maura Isles and Detective Jane Rizzoli, who swiftly link the victim to controversial celebrity psychiatrist Joyce O'Donnell-Jane's professional nemesis and member of a sinister cabal called the Mephisto Club.
On top of Beacon Hill, the club's acolytes devote themselves to the analysis of evil: Can it be explained by science? Does it have a physical presence? Do demons walk the earth? Drawing on a wealth of dark historical data and mysterious religious symbolism, the Mephisto scholars aim to prove a startling theory: that Satan himself exists among us.
With the grisly appearance of a corpse on their doorstep, it's clear that someone-or something-is indeed prowling the city. The members of the club begin to fear the very subject of their study. Could this maniacal killer be one of their own-or have they inadvertently summoned an evil entity from the darkness?
Delving deep into the most baffling and unusual case of their careers, Maura and Jane embark on a terrifying journey to the very heart of evil, where they encounter a malevolent foe more dangerous than any they have ever faced . . . one whose work is only just beginning.

"From the Hardcover edition."