Grade: B+

When Harry was a child, to mangle Paul, he acted as a child, and the movies about him were clearly aimed at the kids; now that he’s growing up, the Potter franchise has matured, too–appreciably, in fact. The first two pictures based on J.K. Rowling’s astonishingly successful series of books about a young sorcery student were doggedly literal renderings of the originals, crowded with incident in apparent fear that fans would recoil in horror at the slightest omission or alteration, and directed by Chris Columbus with plodding determination but little sense of wonder. “Harry Potter and the Prisoner of Azkaban” breaks the mold, and the change is all for the better. Much of the credit must go to Alfonso Cuaron, the Mexican director whose “A Little Princess” (1995) was a captivating treat for young and old alike. Working with screenwriter Steve Kloves (who also adapted the first two films, “The Sorcerer’s Stone” and “The Chamber of Secrets”), production designer Stuart Craig, art director Neil Lamont and cinematographer Michael Seresin, Cuaron has fashioned a visually ravishing, narratively crisp treatment that represents a major advance on the earlier installments.

“The Prisoner of Azkaban,” of course, deals with the third year of Harry’s studies at Hogwarts School of Witchcraft. Having escaped the cruel summer guardianship of his unloving relatives, the now thirteen-year old sorcerer-in-training, again played by bespectacled Daniel Radcliffe, is whisked by ghostly transport back to his real home at the school, where he enjoys the comradeship of pals Hermione (Emma Watson) and Ron (Rupert Grint) and the tutelage of Headmaster Dumbledore (Michael Gambon, taking over for the late Richard Harris) and Professors Snape (Alan Rickman) and McGonagall (Maggie Smith) and forester-promoted-to-instructor Hagrid (Robbie Coltrane), as well as the enmity of his student rival Malfoy (Tom Felton). This year, however, proves even more dangerous to the precocious Harry than his earlier ones, since he learns even before reaching Hogwarts that Sirius Black (Gary Oldman), a wizard imprisoned for aiding the supremely wicked Lord Voldemort in the murder of Harry’s parents, has escaped with the apparent goal of killing their son, too. Happily the youngster is befriended by the deceptively mild-mannered new Defense Against the Dark Arts instructor, Professor Lupin (David Thewlis), who not only saves him on several occasions but teaches him some useful methods of protecting himself. (As readers will already know, Lupin also harbors some deep secrets, one of which is telegraphed by his surname, at least for those who know a bit of Latin.) Less pleasantly, the escapee is pursued by terrifying jailers called Dementors, who pose a serious threat to Harry as well.

The plot complications that follow are considerable, involving other special effects critters in addition to the Dementors–a Pegasus-like steed called a hippogriff and a lycanthrope among them (though the latter isn’t realized as effectively as one might wish)–and more teachers, most notably dotty Professor Trelawney (Emma Thompson), who offers lessons in divination. A turn toward the end, moreover, is predicated on an elaborate time-travel scheme that may prove overly complicated for smaller viewers. But despite the narrative intricacies, Cuaron manages to keep the story moving forward without collapsing in confusion, aided immeasurably by Seresin’s fluid, often soaring camerawork; and though the director can’t entirely smooth out the necessarily episodic structure, he does a far better job of masking it than Columbus did. He’s also fashioned a lush look for the picture, emphasizing a subdued color scheme and more shadowy compositions that complement beautifully the darker tone of this installment of Rowling’s ongoing epic.

The three stars of the series have grown in their parts, too–and not just in the predictable physical sense. Radcliffe, who seemed more than a little stiff in the earlier pictures, comes into his own here, making Harry a convincingly complicated young man (understandable, in view of his unhappy family history). Watson and Grint exchange places from the second film; she was in the background in “Chamber,” while he took a larger role in the action. In “Prisoner,” he has less to do and she more, but both carry off their assigned tasks confidently. Rickman continues to vamp it up delightfully as Snape, and Coltrane remains a pleasantly imposing Hagrid; but Smith is underused, and Gambon makes little effort to imitate Harris’ Dumbledore, portraying the headmaster as an earthier, less ethereal figure. In a small role, Thompson proves herself as capable of extravagant overacting as her ex-husband Kenneth Branagh did as the vain Gilderoy Lockhart in the last film, and Timothy Spall in so convincingly rodent-like as Peter Pettigrew, an important figure in the last reel, that anyone casting the dormouse in “Alice in Wonderland” need look no further. The real find among the new actors, however, is Thewlis, who does a relaxed, refined turn as Lupin, making the character attractive while maintaining an aura of vague suspense about him. Oldman, unfortunately, is curiously anonymous as Black. Except in flashbacks, the role doesn’t call for the rabid nastiness in which he specializes, and his attempt to underplay proves surprisingly dull.

But the heart of “Harry Potter and the Prisoner of Azkaban” turns out not to be the relationship between the two title characters, but the one between Harry and Lupin, and under Cuaron’s sensitive direction Radcliffe and Thewlis give it a depth that was lacking in the earlier films. The result is a picture that might actually appeal to grownups more than children, and (given the streamlining involved in the adaptation) to those who haven’t read the book more than those enamored of it. But since the young sorcerer effectively comes of age in this installment, it’s only just that the cinematic series should do the same. “The Prisoner of Azkaban” isn’t just a good Harry Potter movie; it’s a good movie, period.