Harry Potter and the Prisoner of Azkaban

Sirius Black escaped from Azkaban to pursue Peter Pettigrew, who he believed was hiding in Hogwarts. Though convicted for murdering Pettigrew and betraying James and Lily Potter, Black was actually innocent, the real culprit was Pettigrew himself, who had framed Black and gone into hiding as Ron's pet rat Scabbers.

Peter Pettigrew was a friend of James and Lily Potter who secretly betrayed them to Lord Voldemort, leading to their deaths. He then murdered a random bystander, faked his own death, and framed Sirius Black for the crime. To avoid capture, Pettigrew used dark magic to transform into Ron's pet rat Scabbers and lived as a pet for twelve years.

Hermione's Time-Turner allows users to travel back in time in one-hour increments. Using it, Harry and Hermione travel back three hours before the events at the Shrieking Shack. They rescue Buckbeak from execution and position themselves in the forest to cast a Patronus that drives away the Dementors, saving Sirius from the Dementor's Kiss.

Dementors feed on human happiness and hope, leaving victims with feelings of despair and trauma. Harry is particularly vulnerable because he experienced profound loss as a baby when his parents were murdered. The Dementors draw out his worst memories, including the moment he heard his mother's death, causing him to faint more easily than others.

Sirius Black was Harry Potter's godfather and one of James Potter's closest friends. He was also a trusted member of the Order of the Phoenix. After James and Lily were betrayed by Peter Pettigrew, Sirius was wrongfully convicted of Pettigrew's murder. He broke out of Azkaban specifically to clear his name and protect Harry.

Remus Lupin is a werewolf, a condition he has had since childhood. He takes Wolfsbane potion to control his transformations during the full moon. However, on the night of the confrontation at the Shrieking Shack, Lupin had not taken his potion, either intentionally or through oversight, and transformed when the full moon rose, putting everyone in danger.

Harry cast the Patronus himself, but from the future. When Harry and Hermione use the Time-Turner, Harry positions himself in the forest and casts a powerful Patronus Charm to drive away the Dementors attacking his past self, Ron, and Hermione. This creates a closed time loop where Harry saves his own life.

Buckbeak was sentenced to death after Draco Malfoy provoked him during Hagrid's Care of Magical Creatures lesson. When Draco got too close and insulted the Hippogriff, Buckbeak attacked him, leaving a deep scratch on his arm. The Ministry deemed Buckbeak too dangerous, despite Hagrid's protests, and ordered his execution.

The Marauder's Map is an enchanted parchment created by James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew during their schooldays. It shows every person in Hogwarts, their exact location, and reveals secret passages throughout the castle. Harry uses it to discover the hidden passage leading to the Shrieking Shack where Sirius is hiding.

Harry doesn't actually see his father, the figure he sees is himself from the future. When Harry and Hermione travel back in time using the Time-Turner, Harry casts the Patronus that drives away the Dementors. To his past self, the Patronus appeared as a stag (the same form as James Potter's Animagus form), leading Harry to believe he saw his father.

Cornelius Fudge orders Dementors to guard Hogwarts after Sirius Black escapes from Azkaban. Fudge believed Black was dangerous and intended to reach Hogwarts to harm Harry. The Dementors were meant to provide security, though their presence created a tense atmosphere and negatively affected the students, especially Harry.

Sirius Black escapes capture but remains a fugitive. Harry and Hermione use the Time-Turner to rescue him from the Dementor's Kiss, allowing him to flee on Buckbeak. However, without Peter Pettigrew exposed as the true culprit, Sirius has no way to clear his name and must remain in hiding, though he is now free.