A Catholic miracle story--set in Frenchmen's Bay, Mississippi, in 1950, and nearly saved from treacly indigestibility by some down-to-earth dialogue, an ambivalent finale, and this first-novelist's highly serviceable storytelling equipment. The new boarder at the Our Lady, Star of the Sea convent school is ten-year-old Guinevere Simpson, whose rich alcoholic mother is taking off for a rest-cure, romance, and Nassau. In no time at all, solemn, wee, under-mothered Gwen is on a chatting basis with the outdoor shrine statue of the Holy Mother, who tells her, among other things, to ""Follow the Yellow Brick Road."" The nuns and priests are rather skeptical about Gwen's reports, of course, until: the star of the school's Wizard of Oz production breaks her leg, allowing Gwen to take over brilliantly; a crab-fisherman finds his nets astonishingly full when Gwen gives the nod; Gwen refuses to leave the shrine during Hurricane Agnes (""I'm supposed to be here""), miraculously surviving with no ill effects except a certain aura. Finally Gwen's mother sees the ultimate proof--the statue's plaster hand closes around Gwen's little paw. Not only is this scenario cornily bland; religious people may find the implied equation between the Wiz and things spiritual downright unseemly. However, Haldeman's shorthand sketch of convent-school life is sharp and amusing, with nuns who talk like human beings, gathering in the middle of the night to shoot the breeze (""The convent chapter of Insomniacs Anonymous is meeting in the lavatory""). One nun in particular has an unusual response to the Miracle, supplying an intriguingly off-key coda: ""To me she's still a rather dull, understandably neurotic little girl. Who is she, after all, that she should always get her way. . . ?"" Interesting--enough so that we'll look forward to Haldeman's return, sans angels.