Harry Potter, Ron and Hermione return to Hogwarts School of Witchcraft and Wizardry for their third year of study, where they delve into the mystery surrounding an escaped prisoner who poses a dangerous threat to the young wizard.
Harry Potter (Daniel Radcliffe) is having a tough time with his relatives (yet again). He runs away after using magic to inflate Uncle Vernons (Richard Griffiths) sister Marge (Pam Ferris), who was being offensive towards Harrys parents. Initially scared for using magic outside the school, he is pleasantly surprised that he wont be penalized after all. However, he soon learns that a dangerous criminal and Voldemorts trusted aide Sirius Black (Gary Oldman) has escaped from Azkaban Prison and wants to kill Harry to avenge the Dark Lord. To worsen the conditions for Harry, vile creatures called Dementors are appointed to guard the school gates and inexplicably happen to have the most horrible effect on him. Little does Harry know that by the end of this year, many holes in his past (whatever he knows of it) will be filled up and he will have a clearer vision of what the future has in store.
In the summer before his third year at Hogwarts, Harry Potter (Daniel Radcliffe) becomes fed up with his horrible aunt and uncle, and after accidentally inflating his visiting Aunt Marge (Pam Ferris), he runs away. Unfortunately, theres much more danger in the wizarding world than Harry thought. Convicted murderer Sirius Black (Gary Oldman) has escaped from the wizarding prison Azkaban. Black is known as Lord Voldemorts most devoted follower, and hes after Harry to avenge Voldemort and finish the job. But not everything is what it seems, and inside of Hogwarts there may just be a traitor.