Tony Hillerman is a national treasure, having achieved critical acclaim, chart-topping popularity, and a sterling reputation as an ambassador between whites and Indians. Fortunately, he's also still a marvelous writer, much imitated but never equaled. The Sinister Pig--his 16th novel to feature Navajo cops Joe Leaphorn and/or Jim Chee--isn't his best book, but it's still a pleasure from the first page to the last. Its plot is almost too complex to summarize, involving the mysterious shooting of an ex-CIA agent, financial shenanigans around oil-and-gas royalties, disappearing congressional interns, exotic pipeline technology, and the cross-border trade in both drugs and illegal aliens. Officer Bernadette Manuelito has left the Navajo Tribal Police for the U.S. Customs Service, patrolling the barren borderlands of southern New Mexico. There, her curiosity and smarts land her in a growing peril that provides much of the book's suspense--and invokes the protective instincts of Sergeant Chee, who still hasn't quite been able to tell her how he feels about her. It's impossible not to care about Hillerman's exquisitely drawn repertory characters, nor to overlook the pleasures of his beautifully crafted and relaxed-seeming prose. In the midst of these virtues are a few warts: several sections are a little flat or awkward, and the villainous plutocrat behind it all is short on plausibility (though lots of fun to hate). But even a lesser Hillerman is still a richer, more sat