Roger, the self-proclaimed Stone Cowboy of the title, is stranded in Bolivia as this absorbing debut begins. A cynical expatriate, ex-drug user and ex-con, Roger has been on the High Plains so long that he's started to fantasize about a return to his assembly-line job in Flint, Mich. With no money and no prospects in sight, however, even that dreary goal lies out of reach. Then he meets Agnes, a prim, dutiful American woman who has come to Bolivia to find her brother, Jonathan. A street magician and drug addict, Jonathan originally came to discover the ""real magic"" (notably absent up north in ""Gringolandia"") that he was certain still infused Bolivian culture and myth. Then he vanished. Reluctantly, Agnes allows the savvy Roger to help track Jonathan down, and they soon discover that Jonathan, called Flame by the locals, is the personal magician for Bolivian drug lord El Gran Moxo. Roger and Agnes relentlessly pursue Jonathan against the wishes of sometimes violent players in the country's drug subculture--Americans and Bolivians alike. Meanwhile, they begin to fall in love. If this sounds familiar, it is: Bogart and Hepburn would have played the lead roles in a 1950s film version. Fortunately, Jacobs (author of the story collection A Cast of Spaniards) breathes new life into the old form with lucid, sinewy prose and an intimate knowledge of the Bolivian people and landscape. 20,000 first printing; author tour. (Sept.) FYI: Jacobs is a foreign service officer with experiences in Turkey, Bolivia, Paraguay and Honduras. He is presently cultural attache at the U.S. embassy in Madrid.