What's Up With the Ending?
The Azkaban Redemption
It was a lot easier to get out of Shawshank than it is to get out of Azkaban.
While we're not sure how Sirius broke out of the wizard prison, his journey isn't done yet. While attempting to catch the true villain (the rat Peter Pettigrew) Sirius runs the risk of not just being recaptured and re-imprisoned, but being subjected to the Dementor's Kiss. We'd rather kiss Aunt Marge. With tongue.
To secure Sirius's freedom, Harry and Hermione (mostly Hermione) must travel back in time and prevent the execution of Buckbeak the hippogriff, which supplies Sirius with a handy getaway vehicle.
(If you want to check out a baller analysis of the time travelling aspects of Prisoner of Azkaban, check out M.J. Young's page.)
But taking the H.G. Wells-iness out of the equation, what does the ending mean to our characters and to the series as a whole?
Probably the most important event is that Harry has a new ally: Sirius Black, his dogfather—er—godfather. And although they're not related by blood, Sirius is the closest thing Harry has to a family member besides the pukesome Dursleys. Sirius has the potential to be the father that Harry never had.
But the story doesn't exactly have a happy ending. Sirius promises that Harry can live with him, but he takes back that promise before leaving. It's hard for a single dad to raise a magical wizard when he's on the run from the law. But Sirius isn't a total deadbeat god-dad. He delivers a fancy broomstick to Harry, ensuring he'll be the fastest kid on the Quidditch pitch.
Hermione: Back On Top
Even though Harry's name is in the title, the ending is significant for Hermione too. Sirius delivers her an amazing compliment.
SIRIUS: You really are the brightest witch of your age.
Hermione's often made fun of or put down because of her intelligence, so this remark comes at a critical time. It's a huge boost in confidence for the young witch.
As for Ron…well, poor Ron didn't have much to do in this one. And even though Harry gained a godfather, Ron lost a pet. See ya, Scabbers.
The movie ends with a nifty credits sequence that gives us a good look at the magical Marauder's Map. The very last thing we hear is Harry saying, "Mischief managed. Nox," which extinguishes the light, and we fade to black.
Night night. Don't let the Dementors bite.