To the delight of her young readers, her publishers and booksellers everywhere, British author J.K. Rowling last week announced that she had delivered to the printers the manuscript of "Harry Potter and the Half-Blood Prince," Book 6 in her phenomenally popular fantasy series. It should have come as no surprise -- although it did, because literary success on this scale is so rare -- that the title at once shot to No. 1 on the best-seller lists of both Amazon and Barnes and Noble, the world's largest online book vendors. Quite a feat for a book that won't even exist until next July 16.

Fans of the series are gobbling up the few crumbs of plot news that Ms. Rowling has let drop ahead of the feast: that neither Harry nor the series' unnerving villain, Lord Voldemort, is the "half-blood prince" of the title; that Book 6 will be shorter than the back-breaking Book 5; and that a major character -- not Harry -- will die in the new book. Not that anyone has been expecting Harry's demise. Ms. Rowling has long promised a seven-book series, and while it might have been acceptable for the Heian Period's Murasaki Shikibu to kill off Genji, her shining prince, before his own tale was over, modern literary convention pretty much forbids such a drastic step.

Meanwhile, the bean counters are focusing on purely pecuniary factoids: how many millions of copies of the new book should fly off the shelves in the first few hours; how much publishers' shares rose last week (the market value of Bloomsbury, which puts out the British edition, jumped 8 percent on Monday); and so on. Clearly, the old Potter magic is still potent. It has become fashionable for highbrow critics to denigrate that magic, calling the earlier books derivative at worst, pedestrian at best. Once again, the sheer pleasure so many people obviously feel at the thought of a new installment makes that minority opinion suspect.