The boy wizard and his homies expected their fifth spell at Hogwarts to be tough... but this is riddikulus! OWL exams are looming, the school is being taken over by a tyrannical new teacher, and - despite Ministry of Magic denials - the evil Lord Voldemort is back in business. Dark times indeed. But with Harry assembling his own secret army, discovering romance and facing a grim prophecy, there's enough action and excitement in J. K. Rowling's fifth adventure to stupefy a Swedish Short-Snout (look it up, muggles).
Ever wondered why there are so few fat kids at Hogwarts, what with only six members of each house getting to play Quidditch and every meal being a Jamie Oliver-choking banquet of cream cakes, sausages and hot buttered toast?
It must be the stress of wizarding - especially if you're in Harry Potter's year. Imagine the pressure of dealing with exams and puberty when your school is under the dictatorship of a power-crazed, pink-clad nightmare called Dolores...
Still, Harry (Radcliffe)is lucky to be there at all. After using magic out of school to despatch a couple of Dementors in the Surrey suburbs, only the intervention of Professor Dumbledore (Michael Gambon) saves him from being expelled.
Exonerated or not, Harry's name is still mud in the wizarding world. His godfather Sirius Black (Gary Oldman) knows how that feels, but he's more worried about the rise of He Who Must Not Be Named (aka Lord Voldemort, aka You Know Who, aka Ralph Fiennes minus hair and nose).
Along with several other familiar faces, Sirius has reformed The Order of the Phoenix... aka the Anti-Voldemort League. Harry wants in. The Order wants him back at Hogwarts.
Feeling alone and useless, Harry vents his anger on his pals Ron (Grint)and Hermione (Watson) To make life worse, the new Defence Against the Dark Arts teacher is the aforementioned Dolores Umbridge (Imelda Staunton), a horrid little bag of Ministry-approved rules, crocodile smiles and pure spite.
But, banishing self-pity with a hearty "expelliarmus", Harry sets up 'Dumbledore's Army', a secret club where volunteers can learn dark arts defence the proper way (no textbooks).
When training's over, first they'll take Umbridge - then they'll give what-for to You Know Who.
Production designer Stuart Craig comes up trumps once again and writer Michael Goldenberg has done a commendable job in paring down the longest book into the shortest film (aye, these days 138 minutes represents 'short').
However, anyone unfamiliar with the novel will struggle to keep up. The film just about gets away with skimming over the art of occlumency and the significance of the Department of Mysteries, but fans will agree that reducing the role of the centaurs to one seemingly irrelevant scene is a major mistake.
And with the focus firmly on Harry, some regulars pay the price. Ron and Hermione are little more than spectators while Robbie Coltrane's Hagrid and poor old Draco Malfoy are practically given the broom.
There's no such trouble with Harry. Having waved his wand on the London stage, Radcliffe is clearly growing in confidence and sex appeal, as evinced by his smooch under the mistletoe with Katie Leung's smitten Cho Chang. It drew an audible 'aah' from the female half of the audience.
The newcomers also fare well... mostly. Staunton's Umbridge is a diabolical delight and Helena Bonham Carter enjoys a suitably screechy debut as Sirius's wicked cousin Bellatrix Lestrange.
Regrettably, Evanna Lynch makes a rather uninteresting Luna Lovegood and Kreacher the nasty house elf is introduced and then ignored.
But in the main, director Yates - best known for TV's State of Play - handles both material and budget cleverly. The effects are many yet subtle, deployed to enhance the plot rather than punctuate it. Of course, there are plenty of show-stopping pyrotechnics too.
It's undeniably a treat for the eye, but with death, betrayal and nasty revelations around every corner, J.K. Rowling's stories just get darker and, well, less fun.
By the time we get to Deathly Hallows, we'll need a lumos charm to see it.