As J.K. Rowling's Harry Potter series has become increasingly dark and complex, filmmakers tackling the source material have found it more challenging to present the stories without compromising the integrity of the novels. This prickly problem first reared its head with 2004's Harry Potter and the Prisoner of Azkaban, the first film in the series to meet with angry rumblings from some Potter-philes.
The fifth and newest installment, Harry Potter and the Order of the Phoenix (henceforth OoP), faces the biggest challenge of all. The source novel was not only the longest of the first five (800+ pages), but it contained numerous detailed subplots and character explorations. For the film, director David Yates for the most part successfully left out what could be excised without making the story unrecognizable — although hardcore fans would argue that any omission, no matter how minor, is inexcusable. Other plot points are condensed or altered entirely (a large list can be found on Wikipedia) for the sake of brevity. The major events are all there however.
Right from the opening Harry and his bully of a cousin, Dudley, face danger at the hands of a pair of renegade Dementors. He repels them through the use of a Patronus Charm, which causes him to be expelled from Hogwarts (underage wizards are not permitted to use magic outside school, least of all in front of Muggles). Harry's expulsion from school and subsequent trial at the Ministry of Magic, the key story elements of the first part of the novel, are unfortunately stripped of much of their emotional impact in the movie.
The meat of OoP takes place at Hogwarts, where a new teacher, Dolores Umbridge (Imelda Staunton), makes life miserable for most of the students and staff. The cruel and dictatorial Umbridge tortures Harry and his friends, while also issuing a seemingly endless series of official decrees banning just about everything that makes school worth attending.