I think you mean Harry Potter and the Order of the Phoenix: is the fifth book in J. K. Rowling's Harry Potter book series. It was one of the most widely-anticipated books of the series, since there was a wait of three years between it and the previous book, Goblet of Fire. It is also the largest book in the series, having jokingly been labelled as heavier than a refrigerator (by Stephen Fry at the Royal Albert Hall event) and used as a benchmark for the size of the next two books. spoiler alert The bores of the summer are particularly annoying to Harry Potter at the beginning of this book. He remains at Privet Drive, wholly cut off from the wizarding world, and constantly hoping to hear any news about the return to power of Lord Voldemort. After running into his cousin, Dudley Dursley, on a walk, Harry and Dudley are attacked by Dementors. Harry drives them off with the Patronus, and is surprised to find Mrs. Figg, his old, cat-loving neighbour, storming up the road toward the two teenagers.
However, she does not yell at the two boys, but instead reveals that she is a Squib who has been watching over Harry since the beginning of the summer; she is furious at Mundungus Fletcher (who was to be watching Harry and Disapparated from the front of 4 Privet Drive).
Harry, Mrs. Figg, and a very ill Dudley walk back to Privet Drive.
The Ministry of Magic sends Harry a letter telling him that he's been expelled from Hogwarts for underage magic. Dumbledore is quick to act, telling the Ministry that they do not have the authority to expel Hogwarts students; so the Ministry sets up a hearing to decide whether or not to break Harry's wand. Harry is informed of this through a number of letters delivered to the Dursleys' house after he performed the Patronus charm.
As Muggles are unable to see Dementors, Dudley assumes that Harry attacked him with some sort of spell. Vernon is ready to throw Harry out, as he has always yearned to do so since receiving Harry, when Petunia receives a Howler.
Before she has an opportunity to open the letter, it bursts into flames, and a menacing voice says, "Remember my last". Petunia then immediately convinces her husband to let Harry remain at Privet Drive. Harry has no idea of what's going on.
After many more days of being locked in his room, a number of witches and wizards (auto denominated the "Advance Guard") come to rescue Harry from the Dursleys' home. They are members of the Order of the Phoenix, an elite group whose members fight Lord Voldemort and the Death Eaters. They bring Harry to their headquarters, the house of the Black family, or 12 Grimmauld Place (London). The Weasleys, Hermione Granger, and Harry’s godfather Sirius Black are there. Harry learns that Voldemort is building an army and is attempting to retrieve a "weapon". Arthur Weasley escorts Harry to his hearing. He is cleared of all charges after testimony from Dumbledore, and from Harry's neighbour, Mrs. Figg.
Later, Ron and Hermione are named prefects. When Harry, Ron and Hermione return to Hogwarts, they are surprised to hear that Dolores Umbridge, Senior Undersecretary to the Minister (and who was at Harry's hearing) is the new Defence Against the Dark Arts teacher. During their first lesson they discover that Umbridge refuses to teach real defence methods and that they will not be performing any spells, only learning Ministry-approved theory (learning in a "risk-free way"). It becomes clear she is really there to spy on and take control of the school and is soon appointed High Inquisitor, arbitrarily imposing rules and regulations (known as "Educational Decrees"). She also harbours racial hatred for "half-breeds", such as centaurs, werewolves and similar creatures. She considers Rubeus Hagrid (a half-giant) and Sybill Trelawney incompetent, and sacks Trelawney (Hagrid is dismissed later). Although Dumbledore is unable to prevent Trelawney's dismissal, he invokes his authority to allow her to remain in the castle and appoints a new Divination teacher - a centaur, Firenze.
Harry has disturbing dreams about running down a hallway and attempting to open a door in the Ministry of Magic's Department of Mysteries, but being unable to. Then one night he dreams that he is a snake attacking Ron's father. He awakens in a panic and tells others, who indeed find Mr. Weasley at the Ministry, suffering from severe venomous snake bites. Harry fears he is being possessed by Voldemort. In response, Dumbledore has Snape teach Harry Occlumency to block his mind from intrusion, but their mutual animosity ends their lessons prematurely.
Due to high number of students who are sceptical to Voldemort's return, Hermione blackmails journalist (and unregistered Animagus) Rita Skeeter into writing a favourable article about Harry witnessing Voldemort's return. Ravenclaw student Luna Lovegood, a close friend of Ginny Weasley, argues with her father to publish the story in his paper, The Quibbler. Furious, Umbridge bans the tabloid from the school, but the story spreads rapidly, gathering support for Harry. Many in the wizarding community also now believe Harry.
Hermione convinces Harry to secretly teach students Defence Against the Dark Arts. Though at first reluctant, Harry finally accepts. They name their clandestine group "Dumbledore's Army", or D.A. for short, to mock the Ministry of Magic, which fears Dumbledore is creating a secret wizard army. When Umbridge uncovers the group's meetings, which was due to Cho Chang's friend Marietta Edgecombe, Dumbledore claims that he organized it. Confronted by two Aurors John Dawlish and Kingsley Shacklebolt (who was not loyal to the Ministry, but to Dumbledore), Minister Fudge, and Umbridge, Dumbledore easily disables them and is spectacularly whisked away by his phoenix, Fawkes. Umbridge is appointed Headmistress and imposes even tighter control. Fed up, the Weasley twins instigate a revolt, causing mayhem throughout the school while the staff pointedly do nothing to help Umbridge regain control. This marks the end of Fred and George's magical education, who now opt to move into their magical tricks and joke shop in Diagon Alley, Weasleys' Wizard Wheezes.
Harry receives a vision that Sirius is being tortured at the Department of Mysteries, although Hermione suspects it may be a trap. Harry desperately attempts to contact Sirius at Grimmauld Place via the Floo Network in Umbridge's office fireplace, but he is caught. Umbridge reveals it was she who sent the Dementors to attack Harry during the summer. As she is about to use the Cruciatus Curse on him, Hermione claims that Dumbledore has hidden a powerful weapon in the Forbidden Forest. She leads Harry and Umbridge into the forest where they encounter centaurs. Umbridge foolishly insults them and an angry centaur picks up Umbridge and carries her off screaming into the woods. When Hagrid's giant half-brother, Grawp crashes onto the scene, Hermione and Harry escape amid the chaos.
Harry, Ron and Hermione, along with Luna, Ginny and Neville fly to the Ministry of Magic on the school's Thestrals, unaware they are being lured into a trap. When they arrive at the Department of Mysteries, they are ambushed by Death Eaters. Voldemort seeks a prophecy contained in a glass sphere there and needs Harry to retrieve it for him.
The students heroically fight the Death Eaters, but they are outmatched. They are nearly defeated, but Order members suddenly arrive to help them. During the ensuing battle, the glass sphere is shattered and the prophecy lost. Sirius is blasted with a spell by his Death Eater cousin, Bellatrix Lestrange, and falling backwards, disappears through a mysterious veiled archway. Remus Lupin restrains Harry, who wants to follow and rescue Sirius, telling him that Sirius is dead. Dumbledore arrives and the Death Eaters, except for Lestrange, are captured. Lord Voldemort appears and duels with Dumbledore as Ministry of Magic employees arrive in time to see the Dark Lord before he Disapparates, taking Lestrange with him. Cornelius Fudge finally admits Voldemort has returned and Harry's interview with Rita Skeeter is reprinted in the Daily Prophet.
Later, Dumbledore apologises to Harry for withholding information over the past year. He reveals the lost prophecy, for it was to him that it was first told:
The one with the power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies ... and the Dark Lord will mark him as equal, but he will have power the Dark Lord knows not ... and either must die at the hand of the other for neither can live while the other survives ... the one with the power to vanquish the Dark Lord will be born as the seventh month dies ... Dumbledore also reveals that, due to when the boy was predicted to be born, Neville Longbottom could also have been the child in the prophecy. Dumbledore believes Voldemort chose to attack Harry because he is a half-blood like himself; Neville is a pureblood. In so doing, the Dark Lord marked Harry as his equal; therefore, there is no doubt that the prophecy relates to anyone but Harry.