Like so many other mystery men these days, the splendid Mr. Hillerman has allowed his detective, Joe Leaphorn of the Navajo Police, to get tangled up with terrorists: a Boy Scout troop is held hostage by a fringe Indian-rights gang whose leader is a madman out for revenge and personal gain. But never mind. The plots out at Monument Valley Navajo Tribal Park ("this whole Short Mountain country ain't worth hitting a man with a stick for") have never been Hillerman's magic. That comes instead from his unhokey Indian population, convincingly mystical (sand paintings and ritual cures play key roles here) but alive to modern ways and talk; from the contrast between highways and mountains, asphalt and rock; and from the quiet, wise presence of Leaphorn himself, unselfconsciously drawing on the best of two clashing cultures. With enough action (Joe survives a fife ordeal) and last-second twists to grab those uninterested in the topnotch atmosphere, Hillman's overdue return (five years since Dance Hall of the Dead) should draw murmurs of contentment from all sides.