(CNN) -- It's a difficult age. Fifteen-year-old Harry Potter (the ever-improving Daniel Radcliffe) is at the mercy of his hormones. He's having trouble sleeping, his guardians -- the Dursleys -- want no more to do with him, and he's threatened with expulsion from Hogwarts after pulling out his wand in public. It feels like the whole world is against him.
Daniel Radcliffe as Harry Potter in "Harry Potter and the Order of the Phoenix."
Of course that's far from the case.
Among Muggles, there's no more popular literary hero. And even in his own realm, Harry has an enviable support group of friends and allies, including the so-called Order of the Phoenix, a motley crew of familiar faces that nevertheless remains mysterious for now. If he can bring himself to put his trust in them, perhaps Harry can also learn to trust himself.
At 870 pages, this is J.K. Rowling's longest book, and by consensus, it's not her best. Director David Yates and screenwriter Michael Goldenberg ("Peter Pan") have been more ruthless with the red ink than their predecessors, for which movie fans should certainly be grateful. In fact, at 138 minutes this is the shortest of the Potter movies to date.
It's also the most somber, beginning with a scary Dementors' attack in a dimly lit underpass and ending with an impressively staged battle between the forces of good and evil in the cavernous, black-tiled Department of Mysteries.
In between, Professor Dolores Umbridge employs all manner of tricks to trip up Harry and his friends. A stooge appointed to Hogwarts by the Ministry of Magic, the evil professor rapidly assumes the position of High Inquisitor in order to root out Dumbledore's supposedly insurrectionary conspirators.
Imelda Staunton ("Vera Drake") is hardly the short, flabby, toad-like Umbridge of the book. A giggly disciplinarian in pink knits, she rather reminded me of Queen Elizabeth II, though I suspect there's a deliberate echo of Margaret Thatcher in the way she pronounces her cruel diktats with a passive-aggressive feminine sweetness.
This despicable, petty government functionary masks her prejudice and sadism in blinkered loyalty to her paranoid boss, Minister of Magic Cornelius Fudge. But as villains go, Umbridge is a poor substitute for you-know-who -- the terrifying and elusive Voldemort. Umbridge is a rotten teacher and dangerously deluded, but in the movie, she is often a distraction from the big picture; it's a fundamental flaw that she's allowed to dominate for long stretches.
For the rest -- regrettably -- the adults mostly take a back seat as Harry sets about teaching practical pro-active magic to his schoolmates for the ever-impending showdown. There's a reduced role for Ron (Rupert Grint) too, though the Weasleys pull off one spectacular fireworks display. Perhaps mindful of feminist criticism, Hermione (Emma Watson) takes the initiative once or twice. Which is nice. Watch I-Reporter give her review of Potter's latest »
Mind you, she's still pretty vapid in comparison with the movie's two most arresting new characters: the friendly but decidedly weird Luna Lovegood (Evanna Lynch), and the not-so-friendly but excitingly freaky Bellatrix Lestrange (Helena Bonham Carter in banshee mode).
An experienced BBC TV director, Yates makes a reasonably strong showing on this difficult assignment, but like most of the earlier films in the series, it feels more like potted "Potter" than a movie in its own right. There's still enough suspense built into the saga to keep us watching, but after five installments, this dazzling box office wizard is slowly running out of tricks. There's less wonder here, and less fun -- not even a Quidditch match. In its place is a prevailing sense of grim determination.
Like I said, it's a difficult age.
"Harry Potter and the Order of the Phoenix" is rated PG-13 and runs 138 minutes. E-mail to a friend
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