In Tony Hillerman's The Shape Shifter, a lot is riding on a little mysterious carpet. Not any old welcome mat, but a precious Navajo tale-teller rug, full of portents, interwoven with bits of bark and feathers. Supposed to have been burned in a fire years before, the priceless artifact turns up in the pages of an interiors magazine, shown on the wall of a rich man named Jason Delos. After it's spotted by Joe Leaphorn, a retired Navajo policeman, and an old colleague of his (whose car almost immediately plunges down a canyon), the story ravels through an elaborate investigation of theft and murder. The gentle style of this laconic author and his even more laconic Leaphorn are immensely appealing, as are his insights into Navajo behavior, such as a reluctance to interrupt when anyone is speaking. Hillerman is unbeatable at the flat planes of realistic conversation. One of the most memorable characters is Tommy Vang, a curiously ambiguous, fine-boned man, whom Delos had adopted as a child in Cambodia. He's subtly rendered as something between a sex-slave and servant, and Hillerman uses Vang's gradual recognition of his own situation to propel the story to an exciting conclusion. For readers bent on the whodunit aspect, the title offers a whopping clue, but The Shape Shifter has more to offer than mystery.