"CITY OF DARK MAGIC." by Magnus Flyte. Penguin. $16.The foreign city you have not yet visited glitters in your imagination with the ghost-light of the uncanny. It floats before you, wreathed in a fairy glamour cast by travel magazines, half-remembered spy novels, and drunken stories someone's roommate told you once at a dinner party. You see yourself strolling confidently through spice markets ablaze with color, or blithely navigating labyrinthine cobblestone streets, or flirting over a cloying Muscat with a pliant, sloe-eyed local who grows his own, say, pomegranates or whatever.