It's Harry's (Daniel Radcliffe) third year at Hogwarts and before it even starts, events are already piling up.
First, he has his Aunt Marge (Pam Ferris) blow up and fly away. With the certainty of suspension, Harry flees his home with the Dursleys. He is then picked up by the Knight Bus and taken to the Leaky Cauldron.
There he learns that Sirius Black (Gary Oldman) has escaped from Azkaban to find and kill him.
While the Dementors spread fear and terror in the school, Harry and his friends, Ron (Rupert Grint) and Hermione (Emma Watson), begin to get to the bottom of what is happening.