A horror novel from consistently bestselling Saul ( Suffer the Children ; Hellfire ) is set in Silverdale, Colo., a company-town variation on Spielberg surburbia. There, conglomerate TarrenTech provides the high school teams with every advantage, including a high-tech sports clinic. Dr. Martin Ames beefs up the brawny, aggressive teenagers, and it's to him that newcomer Sharon Tanner goes for answers when her gentle son Mark turns into a belligerent jock overnight. This slick, high-concept thriller, which might have been titled Stepford High , won't surprise anyone, but it should please the author's fans as it continues Saul's focus on children as the vehicles and victims of unnatural forces. 100,000 first printing; $100,000 ad/promo; Literary Guild selection.