Perhaps because of its position as the penultimate installment of a seven-book series, "The Half-Blood Prince" suffers, at moments, from an excess of exposition. Some of Dumbledore's speeches to Harry have a forced, summing-up quality, and the reader can occasionally feel Ms. Rowling methodically setting the stage for developments to come or fleshing out scenarios put in play by earlier volumes (most notably, "Harry Potter and the Chamber of Secrets," with its revelations about the young Voldemort, a k a Tom Riddle).

Such passages, however, are easily forgotten, as the plot hurtles along, gaining a terrible momentum in this volume's closing pages. At the same time, the suspense generated by these books does not stem solely from the tension of wondering who will die next or how one or another mystery will be solved. It stems, as well, from Ms. Rowling's dexterity in creating a character-driven tale, a story in which a person's choices determine the map of his or her life - a story that creates a hunger to know more about these people who have become so palpably real.

The good news is that Harry is courageous and true. The bad news is that Voldemort's agents have more than Peruvian Vanishing Powder on their side. This is a book for children of mettle. It will reward them richly, but they must not whine; they too must be sunny and true and above all brave. The ending is almost too much to bear. I haven't cried so hard since Charlotte the Spider died.

But in Harry Potter and the Half-Blood Prince (Scholastic; 652 pages), the sixth novel in the Potter series, she weaves a remarkable number of narrative threads into a complex, moving and elegantly balanced whole, without any apparent effort.

But Half-Blood Prince turns out to be something else: an elegant, fugal tapestry in the mode of Prisoner of Azkaban. "And now," as Dumbledore says to Harry, "let us step out into the night and pursue that flighty temptress, adventure." It's a tribute to Rowling's dramatic instincts that this actually sounds pretty cool in context.

You can't help but feel that Rowling is trotting out the fan favorites--your Tonks, your Luna, your Buckbeak, your Fred and George--for a final sunlit outing before chaos overtakes Harry. Having carefully built a cozy fictional universe over five previous books, Rowling has the task of tearing it apart.

As Harry himself is becoming more of an adult, so is the tone. It used to be traps and giant creatures with a whispering promise of evil intent to come. But now the game is truly afoot and it's announced with the crack of Harry's nose breaking in the first few chapters.

And yet somehow, in this more adult and dangerous world through which Harry is plotting his way, the writing remains beautifully simple. It flows nicely into your brain and you can see why those learning to read find it easy to digest.

You could argue that it's getting a little too grown-up for its young audience. But I think that maybe a work like this prevents itself from falling into the wrong hands by its sheer size - if you can manage to read your way through 600 pages, you're probably old enough to handle it.

Suzy Feay in the Independent on Sunday called JK Rowling's effort "wordy, flabby and not very well edited".

Robert McCrumb writing in The Observer said her "prose ran the gamut from torpid to pedestrian".

But he added "her plot - driven by the quest for the identity of the Half-Blood Prince - always clips along inventively".

In the Mail on Sunday, James Noble, 10, wrote: "I thought the beginning of the book was a bit boring because all the characters were doing was talking."

BBC News website's Darren Waters read the Half-Blood Prince in less than six hours.

He said: "Too much of the book was either a repeat of what we have seen before, or bogged down by Rowling's attempts to manoeuvre plot lines and characters into position.

"After a while all magic tricks begin to lose their impact."

Rosie Jenkins, 10, said the book "immediately plunges the reader into a world that is grim, chaotic and action-packed".

She added it was "darker and more alarming than the others but that makes it more interesting and impossible to put down".