It Happens in the Dark, by Carol O'Connell

Even though this might not be the best Mallory novel (that's probably Find Me), it is still a pleasure to be back in the company of Mallory and the other members of Major Crimes and the die-hard members of the Thursday-night poker game.  The story centers around a group of mad, drug-addled, and vicious theater troupe members and the evil that they do to one another.