Perseus Academic: Nowhere Land by A.W. Hill

After a member of the Jehovah's Witness Church is abducted in conjunction with a ritualistic triple homicide in the mountains outside of Los Angeles, the church engages cult specialist Stephan Raszer to track her perilous trail. Based on evidence that the girl may have been trafficked into a sex and terrorism underworld, Raszer soon unveils an inside-out reality that begins online and ends in a fabled fortress on the borderlands of Turkey, Iran, and Iraq, where a powerful figure known as Old Man is in control.

With the dubious aid of the abductee's sister, along with a renegade CIA agent and a fraternity of gamesters, Raszer journeys far from the rational world and deep into a dangerous and erotically charged netherland. Raszer learns of a criminal conspiracy linking an ancient Persian sect to an Internet role-playing game used to recruit its foot soldiers. To find the girl, Raszer must play the game, holding on to his soul and sanity in a world turned on its head.