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.

Plot
J.K. Rowling's third book opens with Harry Potter enduring another tiring summer at the Dursleys', which is broken only by a visit from Vernon's sister, Marge. When Marge viciously insults Harry's family, he loses his temper and inadvertently inflates her with a magic spell, causing her to float away. Furious and distressed, Harry decides to run away. While resting, 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, to his surprise, and he proclaims Harry to be in no trouble at all. While staying at the Leaky Cauldron, Harry overhears Mr. and Mrs. Weasley arguing over whether he should or should not be warned about Sirius Black, an escapee from Azkaban, because they believe that Black is hunting Harry, with the intent to kill him.

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.

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. 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. After Christmas, Ron discovers Scabbers is missing, and he blames Crookshanks. Shortly before Christmas, the Weasley twins gave 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 also heard that 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 makes a prediction that the Dark Lord's servant will return to him that night. Harry is puzzled, but goes to bed. A while later, the trio learn that Buckbeak, Hagrid's beloved hippogriff, will be executed for attacking student Draco Malfoy. When they visit Hagrid to console him, Scabbers appears, bites Ron, and Ron chases him to the Whomping Willow. A large dog then 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 he discovers, is an unregistered, and therefore illegal Animagus, a person that 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. They also say that Pettigrew is Voldemort's servant, and he betrayed the Potters, framing Black for the crimes. Pettigrew was also revealed as 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 that when he discovered that Pettigrew was still alive, he 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.

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 Lupin in his werewolf form. 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 along with Black. They are the found, and Black is taken to the castle where the Dementors intend to perform the Dementor's Kiss on him, thus sucking out his soul.

While Harry recovers in the infirmary, 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.

Pre-release history
Of the first three books in the series, Prisoner of Azkaban took the shortest amount of time to write - Harry Potter and the Philosopher's Stone took five years to complete and Harry Potter and the Chamber of Secrets needed two years, while Harry Potter and the Prisoner of Azkaban was written in one year. Rowling's favourite aspect of this book was introducing the character Remus Lupin.