Sweep away the trivia of teenage gossip and then search in your dustpan for the plot: a thirteen-year-old with a bad temper thinks she's a witch until her secret crush suddenly comes up with a premature proposal and the foolproof test--crossing a running stream--which exercises her obsession. All the little sentimental problems of our witch's small-town friends and family are recorded by her slang-poisoned pen and--need we add?--solved with the aid of her ""supernatural"" powers. Some bits are funny but not enough to redeem the fundamental vapidness of the whole. Comments Witchy: ""All at once...I had a sneaking idea that I had known I was ridiculous all the time."" So did we.