With regard to the near-impossible task of making a Harry Potter film that captures all the magic and cleverness of its source material, "The Prisoner of Azkaban" succeeds more thoroughly than either of its predecessors. It is darker and funnier than "The Sorcerer's Stone" and "The Chamber of Secrets," and in nearly every way a better movie.

The difference, of course, is in the direction. Chris Columbus was never more than a serviceable director, offering average entertainment such as "Mrs. Doubtfire" and "Home Alone" before delivering his overly faithful adaptations of the first two Harry Potter books.

Now we have Alfonso Cuarón, a genuinely talented filmmaker ("Y Tu Mama Tambien," "A Little Princess") with a creative eye and a fresh vision. Where Columbus was content to make films that told the stories from J.K. Rowling's novels without distinction, Cuarón uses camera angles, sight gags, scary special effects and (above all) a lively pace to make "The Prisoner of Azkaban" every bit as good a MOVIE as it is a book adaptation. The other films felt like nothing more than companion pieces to the novels, illustrations to go along with the words; this one stands on its own.

Chew on this: The third book in the series is 100 pages longer than the first two, yet the third film is a good 20 minutes shorter -- and still, nothing significant is missing. What Cuarón and screenwriter Steve Kloves (who adapted the other films, too, though apparently with more freedom) have done is streamline the story. Where a book can have events add up over the course of, say, two evenings before coming to a head, it makes more sense for a film to condense the action into one scene. "Azkaban" does this repeatedly, thus finally satisfying fans who want the same flavor and plot lines as the books, while not trying the patience of moviegoers who are perhaps not as rabid in their devotion to the novels and who simply want a solid, well-focused film.

Harry's (Daniel Radcliffe) third year at Hogwarts School of Witchcraft and Wizardry finds him and his fellow students on edge because notorious murderer Sirius Black (Gary Oldman) has escaped from the inescapable Azkaban prison. Consequently, the Ministry of Magic has sent troops of Dementors -- cloaked, Reaper-like demons who suck the souls out of their captives -- to patrol the periphery of the school.

Sirius Black, it is said, was responsible for the death of Harry's parents and presumably wants to find Harry to finish off the Potters altogether. Harry, meanwhile, deals with the usual problems of a schoolboy: his broomstick breaks, Snape (Alan Rickman) is still on his case, and kind-hearted Hagrid (Robbie Coltrane) is in trouble because one of his odd creatures bit Draco Malfoy (Tom Felton). You know, kid stuff.

As his best friends Hermione (Emma Watson) and Ron (Rupert Grint) have some alone time on field trips to Hogsmeade -- where Harry can't go because his guardians wouldn't sign the permission slip -- he finds a confidante in Professor Lupin (David Thewlis), the new Defense Against the Dark Arts instructor who harbors a dark secret himself. Lupin helps Harry learn how to conjure a Patronus, a protective phantasm that can help him defend himself against the Dementors.

The first chunk of the film and the last chunk -- which involves the manipulation of time! -- are the best, whizzing with sly humor (the Whomping Willow makes occasional appearances) and marvelous special effects. Buckbeak the hippogriff -- part eagle, part horse -- is a wonder to behold, and the Dementors are hideously frightening. The thrill of the Knight Bus -- a high-speed wizard transport service that Muggles can't see -- is captured with a sort of mad energy, and aided by John Williams' whimsical score.

In the middle, things are not as buoyant. The books deliver the events of a single school year in linear fashion, without regard for the story having a clear beginning, middle and end. The films have not yet mastered the art of following that pattern without occasionally feeling like they're not GOING anywhere, and even Cuarón is unable to avoid the trap.

The performances continue to be rich and, where suitable, personable. Gary Oldman and David Thewlis are welcome additions, and Emma Thompson is a hoot as Sybil Trelawney, the addle-pated professor of divination. (I submit that even if she were to play a mass murderer, Emma Thompson would still be unbelievably appealing and likable in the role.)

Only the most hardline fans of the books will object to the minor customizations made for the film. All else will praise its ingenuity, spirit and wicked sense of humor.

Grade: A-

Rated PG, some mild profanity, some scary stuff

2 hrs., 22 min.