Harry Potter and the Prisoner of Azkaban

Harry Potter and the Prisoner of Azkaban is the third novel in the Harry Potter series written by J. K. Rowling. The book was published on 8 July 1999. The novel won both the 1999 Costa Book Awards and the Bram Stoker Award, and was short-listed for other awards, placing it among the most-honoured works of fantasy in recent history. A film based on the book was released on 31 May 2004, in the United Kingdom and 4 June 2004 in the U.S. and many other countries.

Rowling's third book opens with Harry Potter enduring another summer at the Dursleys', which is broken only by a news report about an escaped convict, Sirius Black, and a visit from Vernon's sister, Marge. When Marge viciously insults Harry's family, he loses his temper and inadvertently inflates her, causing her to float away. Furious and distressed, Harry decides to run away. After a bad scare, when Harry believes he sees a black dog staring at him from a clump of bushes, the Knight Bus appears and takes him to the Leaky Cauldron. Minister for Magic Cornelius Fudge is waiting for Harry at the door of the Leaky Cauldron, much to everyone's surprise. Harry is certain Fudge will expel him from Hogwarts for using under-age magic, but, surprisingly, the matter is dropped. While staying at the Leaky Cauldron, Harry overhears Mr. and Mrs. Weasley arguing over whether he should or should not be warned about Black, because they believe that Black escaped from prison with the intent to kill Harry.

There are a few changes at Hogwarts as Harry begins his third year. Hermione is taking a double course load, including some that are taught simultaneously. Two new teachers join the staff: Professor Remus Lupin for Defence Against the Dark Arts and, to Harry, Ron and Hermione's delight, Rubeus Hagrid for Care of Magical Creatures. Lupin's lessons are enjoyable but Hagrid's soon become dreary. During the first class, Draco Malfoy is attacked by the hippogriff Buckbeak after Draco insulted him. Draco's father, Lucius Malfoy, files a complaint against Hagrid who then resorts to teaching them about the extremely boring lettuce-eating animals 'Flobberworms.'

Black is still at large, and so Dementors patrol the school. Dementors drain happiness from anyone nearby, and Harry is particularly affected; he faints during a Quidditch match when they approach him and falls from his broomstick, which flies into the Whomping Willow's reach. Professor Lupin teaches him the Patronus charm to repel Dementors, should they attack him again.

Tension grows between Hermione Granger and Ron Weasley because Hermione's cat, Crookshanks, continually torments Ron's rat, Scabbers. At Christmas, Harry receives a superb Firebolt broomstick, and Hermione suspects Black is the anonymous donor. She reports it to Professor Minerva McGonagall, who confiscates the broom for testing. Harry and Ron are infuriated with Hermione at such a marvellous broom being stripped down. When the broom is returned some weeks later, the two boys try to make up with Hermione, but it goes wrong when Ron discovers Scabbers is missing; Ron blames Crookshanks. Hermione's heavy workload, meanwhile, begins to take its toll on her; she accidentally misses a Charms class and drops out of the Divination class altogether.
The US cover for the book.

Shortly before Christmas, the Weasley twins give Harry their Marauder's Map, a magical document that shows every person's location within Hogwarts as well as secret passageways in and out of the castle. Harry uses a tunnel to sneak into Hogsmeade village where he overhears a private conversation that Black was his parents' best friend and is his godfather and legal guardian. He was the Potters' Secret Keeper and he supposedly divulged the Potters' secret whereabouts to Lord Voldemort and murdered their friend Peter Pettigrew, as well as the twelve Muggle bystanders.

After Harry completes his Divination Exam, Professor Trelawney enters a trance and predicts that the Dark Lord's servant will return to him that night. Harry and Ron finally make peace with Hermione, but the trio soon learn that Buckbeak will be executed. When they visit Hagrid to console him, Scabbers appears, bites Ron, and Ron chases him to the Whomping Willow. A large dog attacks Ron and drags him and Scabbers into a hole at the tree's base. Harry and Hermione follow, finding a tunnel leading to the Shrieking Shack. Inside, Harry confronts Sirius Black, who- as an unregistered, and therefore illegal- Animagus, can transform into an animal at will. Lupin, who spotted the group on the Marauder's Map, suddenly bursts in and embraces his old friend Black. Confronted by Hermione, Lupin admits to being a werewolf and the Map's creator, along with Black, Pettigrew, and James Potter, the latter two also being illegal Animagi (a rat and a stag, respectively). Lupin and Black explain that Scabbers is actually Peter Pettigrew in his Animagus form. He is Voldemort's servant, and he betrayed the Potters, framing Black for the crimes. He was the man that Black was sent to jail for murdering. Harry is skeptical until Black and Lupin force Pettigrew back into his human form. Black explains he discovered that Pettigrew was still alive and escaped Azkaban to seek revenge. Harry stops Black and Lupin from murdering Pettigrew, believing that his father, James, would not have wanted his two best friends to become killers. Snape then enters and tries to capture Black but is blasted into unconsiousness by three simultaineous disarming charms from Harry, Ron and Hermione.

Lupin explains that Black was not the Secret Keeper. The Secret Keeper was actually Pettigrew who was able to convince people that Black was the traitor. It is also explained that the four friends, James, Sirius, Lupin, and Pettigrew, developed the Marauder's Map as a way to sneak out of the castle on nights when there was a full moon. They each transformed into an animal as a way to be with Lupin while he was a werewolf and would spend their time in the Whomping Willow/Shrieking Shack, thus also explaining the Shack's reputation.

As the group heads back to the castle, Sirius Black asks Harry to come live with him, as he is Harry's guardian, permitting Harry to escape his uncle's home forever. However, the full moon rises, causing Lupin to turn into a werewolf. During the ensuing commotion, Pettigrew escapes. Black turns into his dog form to protect the others from Werewolf Lupin. Lupin flees, leaving Black badly injured. As Dementors move in to attack Black, Harry sees a mysterious figure in the distance cast a powerful stag-shaped Patronus, scattering the vicious creatures. Harry becomes convinced it is his father, or at least his father's spirit, who produced the Patronus. He then is attacked by the dementors and passes out. Black is then captured and taken to the castle where the Dementors intend to perform the Dementor's Kiss, thus sucking out his soul.

Hermione reveals to Harry that she was entrusted with a time-travelling device called a Time-Turner, which is how she was able to attend simultaneous classes. Prompted by Dumbledore, she and Harry travel three hours into the past, watching themselves go through the night's previous events. They set Buckbeak free and return to the Whomping Willow. As the Dementors are about to attack the "other" Harry and Black, Harry realizes that the mysterious figure he saw earlier was actually himself. Armed with the new memory of his talk with Black, he casts the powerful Patronus that repels the Dementors. Harry and Hermione free Black, who escapes on Buckbeak as the two return to Dumbledore and resume their normal timeline.

Remus Lupin resigns as an angry Severus Snape, who has a childhood grudge against the Marauders, tells the whole of Slytherin House that Lupin is a werewolf. After Harry says good-bye to Lupin, Dumbledore tells Harry that Pettigrew is now in his debt, a fact for which he may one day be grateful. He also tells Harry that "all four Marauders were on school grounds tonight" and says that James Potter lives in Harry.