Olsen (A Cold Dark Place) deftly juggles multiple plot lines as Cherrystone, Wash., sheriff Emily Kenyon investigates the murder of a local woman while crazed serial murderer Michael Barton, on a cross-country killing spree, terrorizes comely young sorority girls. The dead woman's husband is an arrogant philanderer, but Kenyon lacks solid evidence that he was the one who disposed of his inconveniently pregnant wife in a particularly grisly manner. Meanwhile, Kenyon's ex-partner in the Seattle PD, Chris Collier, is pressuring her to make a decision concerning their ongoing romantic relationship. After one failed marriage and singlehandedly raising her daughter, Jenna, Emily is gun-shy about any kind of commitment. When Barton targets Jenna, tension builds but is diffused by Barton's overly extensive backstory, which humanizes him at the cost of the reader's attention. (Mar.)