Only Child — Andrew H. Vachss

After years on the run, Burke is desperate to return to his native New York, the only way he can reconnect with his outlaw "family." But to survive in their part of the City, where reputation is everything, Burke must take major risks to reestablish his presence. So when a Mafia man contacts him about the murder-as-message of his sixteen-year-old daughter -- the offspring of what he calls an "outside the tribe" affair that he must keep secret at all costs -- Burke's depleted bankroll persuades him to step out of the shadows and do something he hasn't done in years ... actually investigate a crime.
Burke needs cover to penetrate the teenage subculture of the Long Island town where the girl lived and died, so he puts together a crew of gifted role-players, including a pair of lesbian "power exchangers" who market their special brand of sex on the Internet. When Burke himself surfaces as a casting director, seeking tomorrow's stars for a movie to be shot on location, the investigation quickly spins off into uncharted depths. What he discovers is a new kind of filmmaking, a new kind of violence, and a predator unlike any he's ever known. When they meet head-on over a brutal work of cinmavrit, only one of them will survive the final cut.