Prisoner of Azkaban

Harry and his friends Ron Weasley and Hermione Granger return to Hogwarts School of Witchcraft and Wizardry and find security has been tightened because ofSirius Black's escape. The grounds are now guarded by Dementors, dark, sinister beings that drain the happiness of anyone nearby and guard Azkaban prison. They also cause Harry to hear his parents. Professor Remus Lupin, the school's newDefence Against the Dark Arts teacher, tells Harry he is more vulnerable to the Dementors because he has seen genuine horrors in his past. He agrees to teach Harry the Patronus Charm, a shield against the Dementors.

Harry is depressed to learn he will not be allowed to visit Hogsmeade, the local village, because Uncle Vernon refused to sign Harry's form. He is also angry withDraco Malfoy for ruining Hagrid's first lesson as Care of Magical Creatures teacher. Malfoy causes himself to be attacked by Buckbeak, Hagrid's beloved Hippogriff, and his father ensures that Buckbeak is sentenced to be executed in the course of the year. Hermione uses a Time-Turner to travel in time and attend classes held at the same time. Black manages to break into the castle twice, but is unable to reach Harry. Fred and George Weasley show Harry a secret passageway to Hogsmeade and give him the Marauder's Map.

Ron discovers that Scabbers, his rat, has disappeared and believes he has been eaten by Crookshanks, Hermione's cat, causing a falling-out between him and Hermione. Hermione later finds Scabbers in Hagrid's hut when the three of them visit him before Buckbeak's execution. On their way back from the hut, Ron is suddenly attacked by a large black dog and dragged into a passage beneath theWhomping Willow, a magical tree. Harry and Hermione receive a brutal beating from the Whomping Willow before entering the passageway.

Harry and Hermione follow the sounds of Ron's screams and find themselves in an old, boarded-up shack known as theShrieking Shack. They also discover that the dog is Sirius Black, who is an Animagus. Harry attempts to attack Black when Lupin arrives. Hermione confronts Lupin about habits she has observed during her classes with him. She says she figured out that Professor Lupin was a werewolf after completing one of Professor Snape's essays, and the characteristics are similar to Lupin's. Lupin then admits to being a werewolf. Lupin explains that he, Black, Pettigrew, and James Potter, Harry's father, were great friends and wrote the Marauder's Map. To make Lupin's transformations more enjoyable, his friends all became Animagi, humans who can turn into animals at will. The Marauders remained friends after growing up, and when they learned Voldemort was after the Potters, Black became their Secret-Keeper. However, Black then reveals that he had secretly switched this duty with Pettigrew in order to serve as a decoy. Black states Pettigrew is the betrayer and, rather than being murdered by Black, is actually Scabbers. Professor Snape suddenly barges in on the scene and threatens Lupin and Black with his wand, and taunts Black with threats of turning him over to the Dementors. However, Harry, Hermione, and Ron all attack Professor Snape with the same spell, thus knocking Snape out.This allowed Lupin and Black to take Scabbers from Ron and revert him back into Pettigrew.

Pettigrew admits to the story, but Harry stops Black and Lupin from killing him and becoming murderers themselves. Instead, Harry persuades them to take Pettigrew back to Hogwarts in order to clear Sirius's name. However, as they return to the castle, the full moon emerges and Lupin transforms into a werewolf. Pettigrew transforms back into a rat and escapes while Lupin loses control in his wolf form. Black is knocked out by Lupin, who is about to kill Harry when a strange howl alerts Lupin and lures him away from Harry. Harry finds an unconscious Sirius lying by a pond, where Dementors suddenly descend on the pair and nearly kill them. They are saved at the last minute by a strange figure using the Patronus Charm, which Harry believes to have been cast by his father. Harry then passes out.

Harry awakes in the castle to learn that Black has been captured. To save him, Harry and Hermione use the Time-Turner to travel back in time and prevent his capture. Harry and Hermione rescue Buckbeak and re-watch the scenes of the night, until they see the Dementors cornering Harry and Sirius. Harry is determined to see who sent the Patronus, only to realize that it was himself. Sirius is rescued and flees on Buckbeak; Lupin, outed as a werewolf, resigns. Harry stated that Professor Lupin was the best Defence Against the Dark Arts teacher he ever had. Harry is worried that Pettigrew may help Voldemort to return, but Dumbledore says Harry may be grateful that he helped save Pettigrew's life.

[Credit: Wikipedia]