Harry Potter and the Prisoner of Azkaban

Harry Potter is, as usual, spending his summer at the Dursley's house. Uncle Vernon's sister Marge arrives for a visit and at dinner time viciously insults Harry and his parents. Harry's anger and unconscious magical powers cause her to inflate and float away. Expecting to have been expelled from Hogwarts for using magic outside of school, Harry flees. Suddenly, the Knight Bus appears and takes Harry to the Leaky Cauldron. There, Minister for Magic Cornelius Fudge tells Harry he will not be expelled. Harry learns that Sirius Black, who is said to be a supporter of Lord Voldemort, has escaped from Azkaban. He is also informed by Arthur Weasley that Black will likely come after him.

Harry journeys to Hogwarts with his best friends Ron and Hermione; they are now entering their third year. On the train they share a compartment with the new Defense Against the Dark Arts teacher, Remus Lupin, who is sleeping when they enter the compartment. Abruptly, the Hogwarts Express is stopped and a Dementor boards, searching for Black. The creature has a profound effect on Harry, causing him to faint. Lupin awakens and repels the Dementor. At school, Albus Dumbledore informs the Hogwarts students that because Black is at large, Dementors have been set up around the school as a protection. In addition to Lupin's appointment, Hagrid is announced as the new Care of Magical Creatures teacher. As lessons begin, Hermione frequently arrives at their various classes by appearing out of nowhere. Lupin's lessons prove enjoyable,; he teaches useful spells and helps less confident students like Neville. However Hagrid's class does not go to plan; on the first day, Draco Malfoy deliberately provokes the Hippogriff Buckbeak into attacking him. His father successfully has Buckbeak sentenced to death.

During a Quidditch match, several Dementors approach Harry, causing him to fall off his broomstick; Dumbledore slows his descent. Harry then decides to learn how to fight the Dementors. Lupin teaches him to cast a spell conjuring a Patronus to repel will repel a Dementor. A Patronus is the opposite of a Dementor which breeds on unhappy thoughts and bad memories. The happier the thought used to cast the spell, the more powerful the Patronus. After several tries, Harry manages to create a Patronus. Later, Harry attempts to sneak to Hogsmeade without permission, but is caught by Fred and George, who give him the Marauder's Map so that he can enter the village through a secret passage. At Hogsmeade, Harry overhears that Black was his godfather and his parents' best friend. Black is said to have divulged the Potters' secret whereabouts to Voldemort and murdered their mutual friend Peter Pettigrew. Harry vows to kill Black, but is later astonished when he sees Pettigrew's name on the map.

In Divination class, Professor Trelawney enters a trance and predicts that the Dark Lord's servant will return to Harry that night. Harry, Ron and Hermione visit Hagrid to console him over Buckbeak's impending execution. While there, Ron discovers his rat, Scabbers, which had disappeared earlier in the year. While trio is chasing Scabbers, a large dog drags both Ron and and the rat into a hole at the base of the Whomping Willow. Harry and Hermione follow, finding a tunnel leading to the Shrieking Shack. The dog is revealed to be the Animagus of Sirius Black. Lupin arrives as well and upon seeing Scabbers embraces Sirius as an old friend. After being confronted by Hermione, Lupin admits to being a werewolf. Snape appears, planning to catch Black and Lupin and hand them over to the Dementors, but is knocked out by Harry. Lupin and Black explain that Scabbers is actually Peter Pettigrew in his Animagus form. Everything that Black is accused was actually Pettigrew and the pair force Pettigrew back into his human form. Lupin and Sirius prepare to kill Pettigrew but are stopped by Harry, who tells them that it was not what James would have done. As the group head back to the castle the full moon rises, causing Lupin to transform and Pettigrew to escape. Lupin and Sirius fight in their animal forms, until Lupin is distracted, and Sirius and Harry are attacked by Dementors. As Sirius is about to have his soul removed, Harry sees a figure in the distance cast a powerful stag-shaped Patronus, scattering the dementors and saving their lives.

Hermione reveals that she possesses a time-turner, which is how she has been taking multiple classes at once. She and Harry travel back in time three hours, watching themselves go through the night's events. They set Buckbeak free and return to the Whomping Willow. As the Dementors are about to attack the "other" Harry and Sirius, Harry realizes that the person he saw was actually him and casts the Patronus. Harry and Hermione rescue a captured Sirius and give him Buckbeak to escape on, as time equals out again. At the end of the year, Lupin resigns, knowing that people will not allow a werewolf to teach their children. Later, Sirius sends Harry a Firebolt, an extremely fast racing broom.