The real magic of this story is that it’s never as simple as it seems, never moves exactly in the direction you think it must. (Beware what you read or hear about “The Snow Child.” The plot is a fragile crystal of suspense that will easily melt in the hands of enthusiastic fans.) Who is the little girl that Jack spots running through the snowy woods, moving “like a rainbow trout in a stream”? Can it be the snow child that Mabel remembers from the fairy-tale book of her youth? “What she was seeing could not be,” Ivey writes, “and yet it did not waver.”