OotP’s central plot theme is the school being crushed under the hand of Umbridge all the while the Death Eaters and Order joust in secret. Everything else needs to be cut away as much as possible.
(for reference, here’s the chapter summaries:)
http://blogs.salon.com/0001092/stories/2003/06/24/harryPotterAndTheOrderOfThePhoenixChapterSummaryIndex.html
Here’s my start on cutting things down:
We open with Harry on trial, defending himself against Fudge. This scene gives us everything we need to establish: that there is a covert war on, that the ministry doesn’t believe Harry, and it allows us to get Umbridge in there from the start. The scene can be altered somewhat to recap the events missing from the end of GoF (Fudge doesn’t believe Voldemort is back: they are all suspicious of Harry for maybe having killed Cedric, etc.), it allows us to recap the Dementor attack without spending lots of time dwelling on it and playing out the scene.
From there, we briefly pass by the Department of Mysteries (we don’t see what Harry will see in the dreams, but a brief glimpse of it as well as the lighting) as yet unmentioned and go right to #12 and Sirus. We establish the Blacks, we establish the Order (Moody, Tonks, Lupin, Mundungus are all we meet, and briefly) they mention that Voldemort is seeking a secret weapon), and we establish the tension between Snape and Sirius. We probably briefly establish Kreacher. Hermoine and Ron are made prefects and Harry is jealous. OWLs are coming up.
From there, right to school, meeting Luna and an awkward bit with Cho again. Harry notices the Thestrals but not much time is spent on it: it’s just something weird (Hagrid relates it later). At the start of term, Hagrid is missing (this is only briefly mentioned). Harry realizes that even the students dont’ believe his story when Seamus rebuffs him. As the official speeches start, everyone expects Dumbledore to speak more but he barely gets a word out when the new order is established and Umbridge’s reign begins (much more obvious and directly taking power than in the book). The sorting hat unexpectedly begins signing its song of unity but Umbridge punches it down and cuts it short. Hermoine says that things don’t look good for this year with the ministry interfering.
And yep: it won’t be: we move right on to DAtDA class: Harry is sentanced to detention for refusing to lie. He meets Cho on the way out of class but Ron spoils it. Back in the common room, the twins are testing out their candies. That night he has his first dream about the as yet unnamed hall of the Department of mysteries: he’s there with Mundungus (minor character but we’ve established that he’s in the order) who is trying to sneak in while he watches (Mundungus seems aware of Harry but with him following orders): but he’s caught by the ministry. Harry’s scar burns and he wakes up.
Mentioning the dream during Quidditch practice to his friends, as well as the realization that he can feel what Voldemort is feeling (that was the scar burning). Hermoine doesn’t understand why one of Dumbledore’s friends would get arrested by the Ministry. Harry is interrupted by Umbridge who is outraged to have him spreading more rumors about Voldemort being back. She bans unapproved group meetings, ends practice, and drags Harry off to his awful detention experience. This is followed up that night by a letter from Percy praising Umrbidge and telling Ron to abandon Harry. Hermoine and Ron bicker and Harry is sick of it. It’s been a terrible day and he’s increasingly sick with his friends. The same dream of the hall again (no events, just the hall, but and this time increasingly creepy with a hint of Voldemort actually being there and watching him).
Harry tries to talk to Dumbledore about the dreams and Umbridge, but Dumbledore mostly kindly rebuffs him, seeming barely interested after catching himself. He does happen to offhand mention a strange room full of (something: exactly what he needed) to another teacher in Harry’s prescence. At the Hogsmede, angry at being brushed off, Harry vents to his friends and Hermoine surprises him: she thinks he should form a REAL DAtDA class and without really asking him (she’s a bit sheepish at this but why would she let THAT stop her: she’s Hermoine!) has invited a whole bunch of interested students. Harry is extremely angry at this… until he sees that Cho is also there.
His final protest later on in the common room is that he doesn’t know where to hold lessons with Umbridge watching everything and banning unapproved meetings. Enter Dobby, and Harry puts 2 and 2 together, finding the Room of Req (its much more flexible than in the books: they have to actually show how it will be filled with whatever one needs). Practice goes well and Neville really starts to shine, as does Ginny who is paying closer attention to Harry. But as they emerge from practice, they run into Seamus, who reveals the Phrophet showing that the Death Eaters have escaped from Azkeban. Seamus is starting to believe Harry more even if other kids still don’t. Neville is with them reading the paper and burns with anger at seeing the faces of the Lestranges (first time we’ve seen them too: they stand out from all the others). Harry realizes that Voldemort is happy, as happy as he’s been in years.
A bloodied Hagrid returns mid-class with Grubblyplank grumpily leaving with Umbridge there. Her bigotry is put on display as he tries to show everyone thestrals (no one can see them, and unlike the books, Hagrid never gets a chance to explain). Umbridge puts Hagrid on notice. Luna can see the thestrals.
Harry goes to bed… his bloodied hand still raw from Umbridge, and dreams of the hallway, being the snake, and Mr. Weasely getting attacked. He rushes to tell Dumbledore who seems shocked and then resigned: after whispering with his portraits (one in particular) he sends Harry and friends straight to the hospital using an unauthorized portkey.
Mr. Weasely is okay, and Mrs. Weasely is overjoyed… yet a little taken aback by Harry. When asked, they say that Dumbledore said not to tell Harry what Mr. Weasley was doing or where he was. Harry and friends listen in with extenable ears after being sent out in the hall: is Harry being possessed? This wonderment is interupted by the appearance of Neville, there to see is parents. Everyone is shocked and sad.
Back at #12, Sirius and Lupin tell Harry about Nevilles parents, Barty (who is mentioned to have been killed by the Dementors) and then hesitently tell him that Dumbledore is having him have lessons with Snape to block his dreams. Harry is angry that Dumbledore can’t just tell him himself and won’t tell him anything, but Lupin angrily insists and Sirius grudingly agrees even though it obviously frustrates him as well. Harry, Lupin, and Sirius all leave on angry terms.
Back at school, a frustrated Harry starts a fight with Malfoy which ends up getting Harry and the twins banned from Quidditch. But the pain is soothed by a great DA class… and the first kiss afterwards with a promise of a date in the Hogsmede. Harry’s mood perks up which carries him happily into his first lesson with Snape. Snape can’t bring his mood down and Harry is defiant, but Snape manages to wrest the image of the MoM from Harry’s mind. Harry suddenly realizes where the hall is: the lighting is the same as what he caught a glimpse of at the MoM.
The next day, the twins are in open rebellion and all hell is breaking loose as their creations terrorize the castle. In the midst of it all, ministry officials arrive to arrest Hagrid for speaking with giants: Hagrid whispers the truth to Harry and Hermoine before he is dragged off against Dumbledore’s protests.
Emboldened, reunited against Umbridge, and now realizing that Voldemort is after something in the MoM, Harry Hermoine and Ron, resolving to bring the truth to light, and Luna provides them with the means to do so. Unfortunately, Harry has forgotten his date with Cho and they have a huge fight over Hermoine. That night he dreams of opening the door and reaching the phrophecy room.
The paper is released with great success and umbridge and her decrees are outraged. Revenge comes: just as the class is learning patronuses, the DA’s cover is blown: Cho squealed (and gets payback from Hermoine’s spell)! Dumbledore is in trouble: the DA has been exposed by the sneak, and he’s also being charged with making an unauthorized portkey. When they try to take him, he flees. The twins also make their grand exit! Harry reveals that winning the Cup came with a substantial reward that he gave to them when it is wondered how they’ll make it out there.
The rise of the Inquisitional Squad begins, and with Dumbledore gone, Umbridge tries in earnest to break Harry, telling him he will never amount to any good and cannot be an Auror. McGonagal overhears and defends Harry, telling him that he will be an Auror no matter what it takes. Lessons with Snape go badly again and Harry catches a glimpse of his father acting like an ass as they battle. Snape throws this realization back in Harry’s face and cancels their lessons and that’s when Harry is hit with his vision of Sirius in the Department of Mysteries. Harry frantically assembles the DA and Luna suggests the thestrals given that Umbridge has everyone’s brooms. As they try to head off to the forest to find the thestrals, Umbridge, the squad, and Snape confront them. Harry tries to clue in Snape, who acts clueless and exasperatedly leaves to get Veritaserum as the triumphant Umbridge requests. Once he’s gone, the invisible thestrals appear startling everyone, a battle ensues, and the DA completely routes Umbridge and the squad as they escape onto the thestrals.
Reaching the MoM, Harry et al get through the spinny room and rush into the prophecy room where the Death Eaters laugh at them. Neville is livid but silent at the appearence of the Lestrange. Harry smashes the prophecies and his friend try to make their escape through all the various crazy rooms. As they run, the Order shows up (Moody, Tonks, Lupin, Sirius) to fight the Death Eaters. Sirius is killed by Bella in the execution room and Harry goes totally ballistic, tearing off after her with an equally vicious Neville in tow. Bella knocks Neville out and Harry starts to use the Cruicio on Bella (much more effective than in the book) but as she screams for her master… he appears. Dumbledore, however, appears to save Harry from him. Voldemorts’ attempt to possess Harry fails, and he escapes as the ministry arrives, and Dumbledore takes Harry away to explain things. As Harry leaves his office, we have the final discussion with Nick and then Luna: that’s just too poingnant to leave out. Harry wordlessly meets his recovering friends who embrace him. End of film.
