by MADELEINE PARTOUS

All true fans of the books have already absorbed Harry Potter and the Half-Blood Prince, and if you haven't read it yet, you probably don't care about plot revelations. Be warned: there are spoilers ahead.

There are two kinds of Harry Potter readers (well, three, actually, if you count the hoards of fabulous weirdniks who write fan fiction on the Net about everything from new plot lines to the so-called "shippers" - ie. relationship fans - who construct wild tales involving any variation of characters from the predictable Ron and Hermione scenario to the more bizarre Harry and Severus Snape connection): kids, of course, for whom JK Rowling can do no wrong, and adults, who tend to overanalyze.

To give them their due, most are apologetic about it. You can't approach Harry Potter without a generous amount of suspended disbelief, but, on the other hand, I've always found that when a book for kids works for kids, it works for everyone.

Harry Potter and the Half-Blood Prince is, as Rowling promised, darker than the previous books and lighter, we're told, than the final one in the series. What's fascinating is that the darker books are still attractive to youngsters - this one's broken all the previous books' sales records in the first weekend - despite the decidedly adult slant. As the series progresses, there's more to it, definitely - but it's arguable that the writing itself, not the plot, is getting weaker.

As the story line gets denser, Rowling seems to be increasingly dependent on an exposition style; I kept thinking, "a little less conversation, a little more action." Just as we've seen in the last couple of books, most of the action happens in the final few chapters.

The blather wears thin, as do the endless romantic intrigues. (To be fair, the book is aimed at an audience for whom adolescent passions are fascinating, so an adult's boredom with the whole thing is probably irrelevant.) Dumbledore pontificates, Harry (who's less grumpy than in Order of the Phoenix, which is refreshing) swoons with lust, and Ron and Hermione still argue endlessly.

And yet here's the rub: it's a great story. As always, we're left wondering whether we've figured out anything at all. The fact is I read the bloody thing in a day and a half and couldn't put it down, warts and all.

For one thing, many things begin to click into place, plot lines we've puzzled over since Harry Potter and the Philosopher's Stone. You can't deny Rowling's obsessive care about the universe she's created. From the first, she's maintained that the entire plot line has existed, at least roughly, in her brain. And part of her vision post Goblet of Fire is that an important cast member perishes in each subsequent novel.

In this one, it's apparently Dumbledore, the headmaster of Hogwart's and the era's greatest wizard, possibly the only hope against the evil of Voldemort. This much had already leaked out - but what few expected is that it would be at the hands of Severus Snape, whom he maintained was a trusted ally despite the doubts of everyone around him.

Most kids will take Snapes's treachery at face value - as Harry himself does, having loathed him since the beginning. Many adults relish Snape because he represents a certain ambiguous dichotomy, which is lacking in other characters who tend to be sharply delineated as good or evil. Let's hope the kids will forgive us for wondering whether Rowling isn't just pulling another fast one. Dumbledore's animal spirit is a phoenix and his body is burned on a byre while phoenix song fills the air.

Here's the final question. Who's right about Snape? Dumbledore, who endlessly insists that he's trustworthy, or Harry and others, who are convinced he's a traitor in the service of the Dark Lord? If the former's true - which would fit with Rowling's complex universe - the phoenix may yet rise from the ashes, à la Gandalf, and live to fight another day.

Harry Potter and the Half-Blood Prince by JK Rowling, Raincoast Books, hc, 672pp, $41