Harry Potter is spending another tiresome summer with his awful Aunt Petunia and Uncle Vernon when a gang of evil spirits called “dementors” mount a surprise attack on Harry and his cousin Dudley. After using magic to defend himself, Harry is visited by a troop of wizards and whisked off to number twelve, Grimmauld Place, London. Number twelve is the residence of Harry’s godfather, Sirius Black, and the headquarters of the Order of the Phoenix. The Order is an organisation of wizards, commanded by Hogwarts headmaster Albus Dumbledore, dedicated to fighting evil Lord Voldemort and his followers. The Order is compelled to operate in secrecy, outside of the jurisdiction of the Ministry of Magic, which is headed by the dense and unscrupulous Cornelius Fudge. Fudge refuses to believe that Lord Voldemort has returned.
Harry utilised magic to fight off the dementors, and as underage wizards are not supposed to use their wands outside of school, he must face a disciplinary hearing at the Ministry. With Dumbledore’s intervention, Harry is cleared and able to return to Hogwarts School of Witchcraft and Wizardry.
Reunited with his best friends, Ron and Hermione, Harry returns to Hogwarts and finds that Dolores Umbridge, an employee of Fudge, will be his new Defense Against the Dark Arts teacher. The Sorting Hat, which usually sorts all new students into one of four houses, cautions the pupils against becoming too internally divided. Meanwhile, the wizard newspaper, the Daily Prophet, continues spreading incorrect and harsh stories about Harry. Many of his classmates are muttering about him behind his back, but Harry ignores them and tries to concentrate on his studies, as all fifth-year students at Hogwarts are expected to take O.W.L.s, or Ordinary Wizarding Level tests.
Umbridge refuses to teach her students how to use Defense spells, and before enough, Fudge names her High Inquisitor of Hogwarts, giving her the right to check all faculty members and judge their competence. In desperation, Harry, Hermione, and Ron organise their own Defense Against the Dark Arts group, often known as the D.A., or Dumbledore’s Army. Twenty-five additional students sign up for the class, and they get together to learn and practise Defense spells as frequently as they can. Harry really wants to talk to his godfather Sirius about the issue, but Umbridge is checking all of the Owl Mail and patrolling the flames that students can use to communicate with wizards living outside of Hogwarts. This makes it impossible for Harry to get in touch with Sirius. Harry Potter is eventually kicked off the Gryffindor Quidditch team as a result of Umbridge’s blatant hostility against him and her belief that he is a liar. Fred and George Weasley, the twin brothers of Ron, storm out of Hogwarts in a fit of protest and move to London, where they have plans to build a joke shop with the money they won from Harry in the Triwizard Tournament the previous year.
Harry has recurring nightmares in which he is travelling down a corridor at the Department of Mysteries, which is located deep within the Ministry of Magic. These dreams are very unpleasant to Harry. When Harry reaches the end of the corridor, he finds a room that is filled with dusty glass spheres after passing through multiple doors. Every time Harry has a dream, he wakes up before he can fully comprehend what it means or what the spheres represent. During one of his sleepless nights, Harry had a vision in which he is reincarnated as a giant snake and attacks Ron’s father. Harry wakes up in a state of abject terror, and Professor McGonagall rushes him to see Albus Dumbledore right away. Dumbledore sends out a signal using the portraits that are hung on the walls of his office, and Mr. Weasley is quickly rescued by two members of the Order of the Phoenix. After that, Dumbledore orders Harry to undergo occlumency classes with Professor Snape. These classes should assist Harry in warding off future mental attacks by Lord Voldemort and protecting his mind in general.
Harry is not very good at Occlumency because he has a hard time emptying his mind of all thoughts. This makes it difficult for him to concentrate on shutting his mind off to any and all outside influences, which ultimately leads to his failure. During this time, Voldemort’s scar, which he received as a result of the incident in which he murdered Harry’s parents, chars brutally whenever he is overcome by an intense emotion. The meetings of the D.A. continue on a regular basis, and Harry’s classmates continue to show significant growth up until Umbridge catches up with them. Dumbledore decides to step down as Headmaster in order to accept full responsibility for the group. Umbridge will now be in charge of the post. The students start taking their O.W.L. tests, and Harry gets another vision, this one of Sirius Black being held captive and tortured by Voldemort. The vision occurs as the students begin completing their exams. Harry, horrified, becomes resolute in his mission to save Ron. Hermione cautions Harry that Voldemort may be trying to deliberately entice Harry to go to the Department of Mysteries, but Harry is too worried about Sirius to take any chances. Hermione warns Harry that Voldemort may be trying to deliberately entice Harry to go to the Department of Mysteries
Harry infiltrates Umbridge’s office undetected and uses the fireplace there to teleport himself to Twelve Grimmauld Place, where he intends to look for Sirius. Harry learns through Kreacher, the elf who lives in the Black home, that Sirius is currently in the Ministry of Magic. When Harry gets back to Hogwarts, he discovers that he and his companions have been arrested for being in Umbridge’s office. Hermione and Harry are successful in persuading Umbridge to accompany them into the forest by stating that they are protecting a weapon on behalf of Dumbledore. When they reach the jungle, the centaurs kidnap Umbridge and take her away. After mounting magical creatures known as thestrals, Harry and his companions flew to the Ministry of Magic in record time. After they have arrived, Harry discovers that Hermione was correct because he is unable to locate Sirius. In addition, Harry observes that one of the glass spheres bears both his and Voldemort’s names engraved upon it. After Harry has taken possession of the sphere, Death Eaters have surrounded him and are preparing to attack while demanding that he hand over the prophesy. Despite using all of their Defense skills, Harry, Ron, Hermione, Ginny, Luna, and Neville only have a decent amount of success against the Death Eaters. However, the appearance of other members of the Order finally provides them with a great amount of assistance. When Harry is in the middle of the battle, he accidentally drops the glass sphere, which causes it to shatter. In the meantime, Sirius’ own cousin Bellatrix Lestrange, a Death Eater, is responsible for his death. Harry is in utter disbelief.
Dumbledore makes an appearance and is able to bring the Death Eaters under control. The moment that Fudge arrives, Voldemort and Lestrange make their getaway. Dumbledore sends Harry back to school and explains that the sphere was actually a prophesy that predicted that Harry possesses a power that Voldemort is unaware of. Dumbledore clarifies that the power that they are referring about is love. The prophecy goes on to say that Harry will either kill Voldemort or be killed by him before the end of the series. Dumbledore makes the most of this chance to explain to Harry the reasoning behind his need to spend the summers with the Durselys in Little Whinging. Harry is endowed with his mother’s love, which is a blessing that can only be sealed by blood because Harry’s mother sacrificed herself to save him. Through the act of adopting Harry into her family, Harry’s Aunt Petunia, who is his mother’s sister, solidifies this connection. Harry is safe so long as he continues to refer to Little Whinging as his home. After hearing this, Harry decides it is best to spend again another terrible summer at his Aunt and Uncle’s house.