I am looking for a fiction book based on plot. It starts in Tucson, Arizona during a monsoon. there is a group of fantasy role players trying out this new AI computer that is supposed to make them feel as if they are their characters. There is a blackout and the technicians are unable to cancel the "game" so they try to unplug one which failed. then they send another person in with a hypnotic suggestion. The players finished their mission and give the code word that forces the AI to release them. Any idea what the book is called. This was read in mid to late 90s.