Harry Potter begins his third year at Hogwarts School of Witchcraft and Wizardry, but dark threats loom over him as an escaped prisoner, Sirius Black, is on the loose.
Sirius Black, a convicted murderer and believed follower of Lord Voldemort, has escaped from the infamous wizarding prison, Azkaban.
The wizarding world is in a frenzy, as it is believed that Sirius is after Harry, putting the school and its students on high alert.
Harry learns about the Dementors, terrifying creatures that guard Azkaban and are now stationed at Hogwarts to capture Black.
Meanwhile, Harry's lessons introduce him to the mysterious new Defense Against the Dark Arts teacher, Professor Lupin, who helps him fend off Dementors.
Harry uncovers hidden truths about his parents’ death, learning that Sirius Black was once his father's best friend and betrayed them to Voldemort.
Through a series of revelations, Harry discovers that Sirius is, in fact, innocent and was wrongly accused, and the real traitor is Peter Pettigrew, disguised as Ron's pet rat, Scabbers.
Using Hermione's Time-Turner, Harry and Hermione go back in time to save Sirius and the magical creature Buckbeak from execution.
Sirius reveals that he is Harry's godfather and asks Harry to come live with him, but circumstances force Sirius to go on the run.
The truth about Sirius remains hidden from the public, but Harry is comforted knowing that his godfather is alive and fighting for justice.