It's a curious fact about Harry Potter's magic that it doesn't really look all that hard to do. You wiggle the wand, you say the words--"Lumos! Expelliarmus! Accio Car Keys!"--and if you're not a Muggle or a Squib, if you've got the right stuff or the midichlorians or whatever, you're in business. How hard is that? And that Hermione Granger is supposed to be some kind of genius.
What J.K. Rowling does doesn't look that hard either. She's not a showy stylist or a Big Thinker, 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. Rowling loves to wrong-foot readers, and the previous book, Order of the Phoenix, reads like the loins-girding preamble to an all-out, good-vs.-evil, wand-on-wand wizard war. 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.
We begin with the eternal, eternally entertaining compulsory figures. It's summertime, and Harry makes his way from the Dursleys' to the Weasleys' to Diagon Alley to Hogwarts (we're spared the Sorting Hat's customary verbosities this year). Snape has at long last secured the Defense Against the Dark Arts teaching job. Draco has his usual generic mischief cooking. Harry, now 16, has been made captain of Gryffindor's Quidditch team, and he has stumbled on a mysterious potions textbook that was formerly the property of--wait for it--a certain Half-Blood Prince. Meanwhile, Dumbledore and Harry, with the help of that always handy expository aid the Pensieve, are poring over the details of Voldemort's early backstory for clues to his intentions. Oh, and somebody's trying to kill Hogwarts students. As Hagrid puts it, with the barest trace of a wink, "Chamber o' Secrets all over again, isn' it?"
For true believers, Half-Blood Prince will be pure pleasure. There's Quidditch, potion-class high jinks, apparition lessons, loads of snogging (Ron and Hermione are slowly sorting out their longtime mutual crush) and some lovely business with a golden potion called Felix Felicis that makes whoever imbibes it extra lucky. But this is the second-to-last book in the series, and for all the fun, the mood is darkening. 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, and there are several tableaux of genuinely surreal horrors, including a vicious werewolf (not at all cuddly like Lupin). The book ends with a shockingly violent reversal that permanently and painfully alters the fixed stars of Harry's life. Which is to say that once again, somebody dies.