Remember Thackeray's tour de force in the realm of fantasy- The Rose and the Ring? Now another English novelist tries his hand at a not unlike type of story, half fantasy, half realism - salted by a slightly cynical sideswipe at some of the fallacies and absurdities of the modern spirit. Probably London's parallel to Madison Avenue will find their toes trod upon. But for the American public the ironies are a bit stretched, the lingo often too British. Taken as a fantasy, a fairy tale, with a modern setting of today's advertising world set against a segment of King Arthur's kingdom in ancient Britain, the two crossing barriers under the power of two magicians in competition- the story is at times funny, more often absurd, and rarely successful in translating one to a world of faerie. A limited market.