When we last saw Harry Potter on screen, he was going through a bit of an awkward phase. Stretchy and pale, the bespectacled young wizard, played by a sprouting-into-adolescence Daniel Radcliffe, appeared to be touched by a force -- puberty -- as unruly as any otherworldly spell. But in Harry Potter and the Prisoner of Azkaban, Harry has come out the other side of his growth spurt and looks all the better for it. He's leaner, more handsome, and bolder than before, and that's true, as well, of the movie itself.
In ''The Prisoner of Azkaban,'' Harry faces down assorted foes, including Sirius Black (Gary Oldman), a scraggly escaped convict who may hold a violent grudge against him, and he does it with an authority he hasn't previously shown. Harry also has interludes of jaunty rapture, like his soaring king-of-the-world flight aboard a Hippogriff (half horse, half eagle). All of this has been staged by Alfonso Cuarón, the Mexican-born director of ''A Little Princess'' and ''Y Tu Mamá También'' (he takes the reins from Chris Columbus), with a breathless visual and dramatic flow that only underscores what buggy contraptions the other two ''Harry Potter'' films were. Shot in spooky gradations of silver and shadow, ''The Prisoner of Azkaban'' is the first movie in the series with fear and wonder in its bones, and genuine fun, too.
The droll enchantment of the ''Harry Potter'' books comes from the way that J.K. Rowling turns a child's wild and woolly dream-world of spells, creatures, and sky-high Quidditch matches into something scruffy and Dickensian: transportingly everyday. That was the quality violated by the first two movies. Columbus staged them like the ultimate Muggle, zapping you with each beastie and wizardly doodad. His tone of mechanized japery said, ''Look, here's the next effect! The next blockbuster money shot!'' What was missing was the flippant and addictive offhandedness that Rowling, in her madcap stew of Roald Dahl, the Hardy Boys, ''Chitty Chitty Bang Bang,'' ''The Chronicles of Narnia,'' ''E.T.,'' and ''Star Wars,'' infused into every page.
Right from the start of ''The Prisoner of Azkaban,'' when Harry confronts a tyrannical aunt by forcing a glass to break in her hand -- shades of Sissy Spacek in ''Carrie'' -- the supernatural in this movie has an emotional anchor, and it isn't belabored. Trying to get to the Hogwarts School of Witchcraft and Wizardry, that magic-mushroom vision of a British prep academy, Harry boards a triple-decker bus for a ride so speedy it's nutzoid, as a shrunken head chatters like a refugee from ''Beetlejuice.'' The whole movie zips along with a matter-of-fact cleverness that stays a step ahead of you.
At Hogwarts, Harry meets several new instructors, like a flighty Divination professor played by Emma Thompson as the most myopic of seers (''Your aura is pulsing, dear,'' she quavers to one student. ''Are you in the beyond?'') and David Thewlis as Professor Lupin, the requisite new Defense Against the Dark Arts instructor. Asked to think of what scares them most, each student readies his or her wand, and the shape-shifting fiend hidden in the cupboard takes the form of their fear -- until it's changed into something laughable. Timid Ron (Rupert Grint) conjures a giant spider; another student calls forth Professor Snape (Alan Rickman), whose dour menace is dissipated when the boy imagines him wearing his grandmother's clothes. As for Harry, his mind drifts toward one of the Dementors -- no, not an obscure group of psychedelic '60s garage rockers, but a chilling phantom with a head like an octopus' and a ghostly body of ashen black. It can suck the soul right out of you, and as it looms up in class, Harry can scarcely contain his tremors. The effects may have come out of a digital lab, but they're never far removed from the characters' heads and hearts.
''The Prisoner of Azkaban'' is still too long, with that slightly arbitrary quality that's better filtered through the fairy-tale tranquillity of Rowling's prose. But Cuarón, streamlining the book and inventing a few marvels of his own (like most of that Hippogriff ride), has gotten Rowling's spirit on screen. You can feel it in the way the paintings on the Hogwarts walls are animated, in every sense, yet never lose their gilded Renaissance glow, or the doleful way Harry emerges from his Invisibility Cloak after hiding out from the world. The universe here is always in flux: A rat turns into a ratty-looking man, and Harry confronts his fears by literally stepping out of time to gawk at himself. By letting him, and the series, grow up a bit, ''The Prisoner of Azkaban'' turns kids' stuff, once again, into serious play.