‘Safe and Sound’ by Laura McHugh. Random House, 304 pages, $29 Small towns can be a sanctuary, offering the comfort of family, friends, familiar surroundings and an assured future. But for sisters Amelia and Kylee Crow, their small town of Beaumont, Missouri, is a trap, holding only a dismal future, as Laura McHugh explores in her outstanding “Safe and Sound.” Beautifully written with precise character studies, “Safe and Sound” joins the growing legion of rural mysteries, where everyone thinks they know everything about their neighbors, but that is far from the truth.