A lively departure for historical novelist Carr (Woman's Own, 1990, etc.), who returns with a competent psycho-mystery suspense novel, set in small-town Colorado, about a woman of a tragic past and scary present who sleuths--with both a lawyer's ken and gut instincts--to bring down a killer. Thirty-seven-year-old Jackie Sheppard--who's been divorced for 12 years from police detective Mike (they're now good friends), and who lost her only child in an auto accident two years ago--joins a law office in the town of Coleman, Colorado. As a newcomer, Jackie is not unhappy to have the genial attentions of attractive carpenter Tom Wahl, and they make love once, after casually dating and trading tragic pasts--Tom's family of wife and two babies were killed when he was a psychologist for a penal system. And the killer is still at large. Then someone is slithering around Coleman, someone who leaves traces in Jackie's locked house. Others report similar invasions, all of which pale when the body of a murder victim is discovered nearby. Forthrightly dumping Tom, Jackie begins to dig for facts, but she ``was dealing with the big X factor, the ever-present missing link....My instincts were charged with warnings.'' The town sheriff, now a pal, ex-husband Mike, and the feds circle the evidence, but it's Jackie--with Tom a large factor--who pins the killer to the mat. (There is, of course, a satisfying final confrontation and rescue, as well as a quick study of a sociopathic serial killer.) Pleasant small-town atmosphere, action, and bothering goings- on. A solid debut for Carr into the psychothriller field, to which she should attract her historical-novel following.