One of the pleasures of reading books in a series is the quick start-up. We already know the characters, we are familiar with the writer's voice, we have a sense of the story, and we are anxious for it to get under way.

	"HARRY POTTER AND THE HALF-BLOOD PRINCE" By J.K. Rowling Scholastic ($29.99)

And so it is with the saga of Harry Potter, which had people all over the world up till midnight July 15, the moment the sixth volume went on sale.

From the start, No. 6 drops us right in to J.K. Rowling's completely convincing and thoroughly engaging world, which we quickly learn is moving ever closer to ours.

Rather than opening with Harry at home with his loathsome relatives, the Dursleys, as the books typically do, this one begins in the office of the British prime minister, who reluctantly takes a meeting with "the other Minister," from the Ministry of Magic.

As we know from the last book, the wizarding community is at war:

Voldemort, aka He-Who-Must-Not-Be-Named, aka the Dark Lord, has rallied his army of followers, the Death Eaters, and the hideous beings, the dementors, have deserted Azkaban prison to join them.

But the trouble isn't confined to the parallel world of magic.

In everyday England, bridges collapse, a freak hurricane hits and a thin, cold mist is spreading over the land. In both realms, everyone blames the government.

Upon learning of the disarray in the wizarding world, the British prime minister exclaims, "But for heaven's sake -- you're wizards! You can do magic! Surely you can sort out -- well -- anything!"

To which the Minister of Magic kindly replies, "The trouble is, the other side can do magic too, Prime Minister."

And in that little exchange we have all the appeal of the story of Harry Potter. We are in a world where anything is possible, because magic is real, but where our own world's fundamental struggles with good vs. evil still apply, to an even grimmer degree.

But a world at war also has a domestic side, and that is where most of the book takes place, within the fortified walls of Hogwarts school.

There is once again a new teacher, but he is there to teach Potions, replacing the ever-inscrutable Severus Snape, who has finally persuaded Dumbledore, the headmaster, to let him teach Defense Against the Dark Arts.

The Half-Blood Prince of the title turns out to be, for most of the book, a book. Harry has borrowed an old textbook inscribed with that name.

He discovers that the previous owner has filled it with brilliant annotations for shortcuts in formulas, for curious hexes and spells, and -- to his friend Hermione's dismay -- Harry begins to trust its guidance.

Harry, Hermione and Ron are now 16, taking advanced courses and learning to "apparate," traveling the way full-fledged wizards and witches do.

Harry's surly moods from the last book have passed, leaving him more mature and responsible, captain of the Quidditch team and less sensitive to what others think.

Draco Malfoy emerges as a more powerful nemesis.

Adolescent love affairs, too, grow more serious: Hermione and Ron spend half the year dating other people, trying to make the other jealous; there's quite a bit of "snogging" (really serious kissing) going on.

At Dumbledore's request, Harry begins to take private lessons, and theirs becomes the most important relationship in this book.

Working from restored memories that they examine, and then inhabit, in the magical Pensieve, Harry and Dumbledore attempt to imagine their way into the life and mind of Tom Riddle, the boy who grew up be Voldemort, from his birth to a witch who was the last descendant of the line of Slytherin, to his days as Dumbledore's student.

That inward journey informs the mood of this installment in Rowling's bigger story. "The Half-Blood Prince" is shorter than the last two books, quieter, more personal.

Rowling works carefully here to bring together strands of the previous books, deepening the major characters, connecting the history of earlier generations and examining the alliances for evil and for good.

The rumors we have heard are true -- a major character dies, and the book ends soberly, sadly, seriously.

We see Harry assuming his mantle as "the Chosen One," determined to bring an end to the Dark Lord. Richly satisfying on its own, this sixth volume seems to function as a rest before the final storm that the next book, projected to be the last Harry Potter, promises.