The opening scenes of Harry Potter and the Prisoner of Azkaban hold to the convention of the books--our hero once again suffering in the suburban cottage of his guardians, the awful Dursleys--but audiences immediately will recognize the big change that marks this third installment of J.K. Rowling's extraordinary series. At 13, Harry has entered into the angst-filled stage between adolescence and adulthood that no amount of magic can ameliorate.

First, there is Harry's new awkwardness, his flopping about in bed between feigned sleep and clandestine, under-the-covers spell-casting, cute if he were still 11 but silly in a preternaturally mature teenager. Then there's Harry's new anger, his sassing Uncle Vernon and Aunt Petunia (Richard Griffiths and Fiona Shaw) before blowing up blowzy Aunt Marge (Pam Ferris, in what can only be described as an inflated cameo). Finally, there's Harry's new attitude, his take-this-life-and-shove-it approach to conflict resolution as he storms out of his boyhood home, trunk packed, trading in Muggledom for Hogwarts School of Witchcraft and Wizardry with a vengeance.

The producers had this transition in mind when they chose Alfonso Cuaržn to replace Chris Columbus as director of the franchise. Having earned acclaim for his work with young actors in Great Expectations, A Little Princess and Y Tu Mamá Tambin, Cuaržn proves himself again by coaxing solid performances from Daniel Radcliffe as Harry, Emma Watson as the clever Hermione Granger, and Rupert Grint as the faithful Ron Weasley.

As the characters age, however, the story grows more somber and serious, at least for the moment. The Prisoner of Azkaban is darker than The Sorcerer's Stone and The Chamber of Secrets, although not without humor. One-liners replace whimsy and the sight gags tend toward the smart-ass shrunken-head variety, but there's still wonder and warmth, supplied in no small part by the giant Hagrid (Robbie Coltrane) and his latest adopted creature, a half-horse/half-eagle Hippogriff named Buckbeak. That said, moviegoers should be prepared for a gruesome werewolf and soul-sucking wraiths--genuinely disturbing stuff for impressionable kids--and a fair amount of discussion about death, fear and loss.

In addition, the plot of The Prisoner of Azkaban is complicated, at times confusing, especially for those unfamiliar with the novel. Having run away from the home he abhors, Harry is rescued by the Knight Bus, a triple-decker, shape-shifting contraption apparently sent to convey him to the Leaky Cauldron pub in Diagon Alley, a magical byway in London. There, he learns that a sociopathic wizard named Sirius Black (Gary Oldman), the wretch said to have murdered Harry's parents, has escaped from Azkaban prison--and is looking for him.

Safely back at Hogwarts, Harry is befriended by Professor Lupin (David Thewlis), the school's new Defense Against the Dark Arts teacher. Lupin trains the boy to use a powerful charm to ward off Dementors, mercenary spooks who have been employed to guard the school even though they exhibit ill will toward Harry, too. If the situation seems mildly confusing, it becomes more muddled after Harry uses his cloak of invisibility to clandestinely roam Hogwarts and the neighboring village of Hogsmeade in search of clues. He learns that a family friend named Peter Pettigrew (Timothy Spall) was also killed by Black; that Black was Harry's godfather before morphing into his mortal enemy; that Pettigrew might not be dead after all; that Lupin might not be his protector...misdirections and false steps run amok, literally, as Harry employs an enchanted Marauder's Map to trace footprints in real time.

Presumably a good portion of the audience will have read the book, so the plot will be as clear as the crystal ball consulted by Professor of Divination Sybil Trelawney (Emma Thompson), who foresees grim times for Harry. The uninitiated, however, had best pay close attention to the film's pivotal scene in the Shrieking Shack, where Harry, Hermione and Ron confront Black and the dour Professor Severus Snape (Alan Rickman). From this point on, the movie involves time travel, doubles and reversals that, while paradoxically easier to follow than the preceding narrative, nevertheless require disciplined attention.

In defense of Cuaržn and screenwriter Steve Kloves, The Prisoner of Azkaban delivers clever twists and ripostes, and the scene in which Lupin instructs his charges to use their powers of imagination to conquer their fears is (as Ron might say) absolutely brilliant. There is a Quidditch match, of course, and the simpering Draco Malfoy (Tom Felton) and his fellow Slitherins do their best to mock their rival Gryffindors. (Note to Rowling: It's time to let Malfoy win one for his house.). Michael Gambon takes over nicely for the late Richard Harris as Headmaster Albus Dumbledore, but we miss Mr. Harris. Needless to say, the CGI is sheer wizardry, as is the score by John Williams.

As for the leads, Grint and Watson emerge from under Daniel Radcliffe's cloaks in this film. Radcliffe, whose voice is changing, seems less comfortable with his role, or perhaps that was his choice. Harry is, after all, under considerable stress, his anxiety compounded by his increasingly lugubrious longing for his lost parents. Meanwhile, Grint has grown more likeable, and anyway, he may be the most talented actor of the trio. For now, though, Watson is the one to watch. Teenage girls are said to mature faster than boys, and exhibit more poise and confidence. That old saw holds true, judging from her performance in this more thoughtful, but still entertaining, Harry Potter.

--Rex Roberts