It is the interesting fate of "Freddy's Book" to follow John Gardner's critical essay "On Moral Fiction" on the ever-longer shelf of his books. Interesting because the new novel is a very enjoyable one, an entertainment high and bright, in every sense; and yet it can't expect to escape the dead-earnest question, is it moral? Its very structure—a novel within a novel, or rather, a fairytale-historical novella with a long fictional preface explaining how the subsequent narrative fell into the editor's hands—suggests the kind of literary game-playing against which the Gardner of "On Moral Fiction" has so much to say: it is a structure worthy of that "unmoral" novelist John Barth. "On Moral Fiction" itself is very enjoyable too—meaning brightly readable, which critical essays generally aren't. But underneath it is a sermon as solemn as the little word "on" in its title, shot through with...