By Nevada Barr (Putnam hardcover, $24.95, ISBN: 0399152415, 3/2005; Berkley paperback, $7.99, ISBN: 0425208419, 2/2006) In Barr’s taut 13th thriller to feature Anna Pigeon (after 2004’s High Country), the 50-ish National Park Service ranger leaves her new husband, Paul, back in Mississippi, to assume a new post in Colorado’s Rocky Mountain National Park, where she encounters a serial killer and a strong, determined woman, Heath Jarrod, much like herself. Heath, a former ice climber now confined to a wheelchair after a near-fatal fall, feels depressed, isolated and helpless. She’s camping in the national park with her physician, who’s also her aunt, when a pair of battered young girls, two of three missing from a nearby religious retreat, ap...