Where, Carlos Fuentes asks, is a modern-day vampire to roost? Why not Mexico City, populated by ten million blood sausages (that is, people), and a police force who won't mind a few disappearances? "Vlad" is Vlad the Impaler, of course, whose mythic cruelty was an inspiration for Bram Stoker's Dracula. In this sly sequel, Vlad really is undead: dispossessed after centuries of mayhem by Eastern European wars and rampant blood shortages. More than...