<P> At Hogwarts, Harry has several problems with the Dementors, including an episode at a Quidditch match during which he faints and falls off his broomstick from high in the air . His broom is blown away and smashed by the Whomping Willow . Working with Harry outside class, Lupin teaches him the Patronus Charm to repel Dementors . </P> <P> On an unauthorised visit to the village of Hogsmeade (thanks to The Marauder's Map, given to him by George Weasley and Fred Weasley), Harry overhears some of his teachers talking with Fudge about Black . They reveal that Black was a friend of Harry's parents but he betrayed them and gave Voldemort access to their house . They also mention that Black killed thirteen Muggles and his former friend Peter Pettigrew . </P> <P> Ron and Hermione's friendship later suffers when Ron believes that Hermione's cat, Crookshanks, ate his rat, Scabbers . At Christmas Harry receives a mysterious present, a late - model Firebolt broom . Fearing it might be cursed, Hermione reports the gift to Professor McGonagall, which leads to more bad feelings between her and Ron and Harry . </P> <P> Ron, Hermione, and Harry join the effort to save Hagrid's hippogriff, Buckbeak, from being executed for attacking Draco Malfoy, after Draco provoked him . Their efforts are unsuccessful, but Scabbers reappears shortly after they hear Buckbeak being executed . </P>

Number of chapters in harry potter and the prisoner of azkaban