Away with youthful follies - the fifth instalment of cinemat ic Pottermania is about serious stuff. Aside from the diversion of a bit of snogging between Daniel Radcliffe's Harry and a female pupil, there's a head-on collision between good and evil to consider and director Peter Yates's luxurious-looking movie considers it from the very first scene.

We start during a parched English summer (global warming, perhaps?) when a vast thunderstorm, enough to put paid to Wimbledon for a week, stops the bullies menacing Harry on the Hogwarts playing fields. Down from the skies come two Dementors - and Harry uses a forbidden curse to fend them off.

Gallery: Harry Potter And The Order Of The Phoenix premiere

Gallery: Harry Potter: Then and Now

This lands him in trouble with the Ministry of Magic and only the intervention of Dumbledore (Michael Gambon) prevents his expulsion. The Ministry just won't believe that the evil Lord Voldemort-Ralph Fiennes, again) is back and imposes the formidable Dorothy Umbridge (a smiling but innately hostile Imelda Staunton), to be the year's professor of the Dark Arts.

What is poor Harry to do? Umbridge puts him in detention, prohibits the learning of practical curses, is thoroughly nasty to the poor eccentric Sybil Trelawney (Emma Thompson, very funny) and confronts Dumbledore in an effort to assert complete control. But Harry's not beaten. He assembles a rebel band called Dumbledore's Army, with Hermione (Emma Watson) playing Che Guevara to his Castro.

But why am I telling the millions who have already read the book all this? Just to reassure them that the book is not betrayed in any major way. There are, however, inevitable omissions, given the book is 870 pages and the film is the shortest of the series.

This is the only Potter film without Quidditch. Also largely absent are the usual ghostly beasties and the Hogwarts factional intrigue. Instead, Yates and new writer Michael Goldenberg go for the jugular.

They are far more interested in engaging us on another, more straight-faced level and Nicholas Hooper's dramatic music, which I dare to prefer to John Williams's more obvious tunefulness, aids them further.

The climactic finale between Harry's lot and Voldemort's gang, led by suitably named Lucius Malfoy (Jason Isaacs), is played out with some panache in a vast Ministry storeroom filled with globes containing prophecies. Voldemort wants one of them, gets it and then ... but I'll say no more.

Is the darker tone of the film something to do with JK Rowling, or Yates's dim view of the world as it is? We'll have to see about that in the last two films and the final book.

Meanwhile, fans will surely savour the high professional gloss and expertise of this film, and the acting of a notable cast (Helena Bonham Carter as mad-eyed Bellatrix and Alan Rickman as Severus Snape, among them). This is a movie that's bound to satisfy most of those who have read the book, and a good many who haven't, too.