Harry, Ron and Hermione learns that a dangerous man, Sirius Black, has escaped from the Wizarding prison, Azkaban, and is supposedly after Harry. The trio masters the spells necessary to confront Black. However, Black is not all he seems: He was convicted of the murder of thirteen people nearly thirteen years ago, but the real murderer, Peter Pettigrew, is hiding in the disguise of Ron's pet rat, Scabbers. Together with Professor Lupin and Black, Harry, Ron, and Hermione unmask Pettigrew, only to have him escape when Lupin turns into a Werewolf. Using Hermione's Time-Turner, Harry and Hermione go back in time and rescue Hagrid's Hippogriff, Buckbeak, and use him to rescue Black.