Our favorite wizard (apologies to the entire cast of Wizards of Waverly Place) is beneath his bedsheets secretly trying to read a book. It's hard for Harry Potter to get anything done in the Dursley household. His reluctant foster parents, Uncle Vernon and Aunt Petunia, hate the boy for simply existing.
We learn that this hatred runs in the veins of the Dursley family (alongside either ice water or turkey gravy) when Aunt Marge visits. She makes the evil aunties from James and the Giant Peach seem warm and cuddly.
After she insults Harry's dead parents, Harry magically inflates Marge like the Goodyear blimp. Afraid he'll be booted from Hogwarts for using magic outside of school, Harry runs away from the Dursley household.
In a nearby park, Harry is almost attacked by a mangy black dog. He's saved in the knick of time by the Knight Bus…which is (k)not what it seems. It's a magic bus, zipping through the streets invisible to the eyes of Muggles. It deposits Harry at the Leaky Cauldron, where the Minister of Magic forgives Harry for inflating Marge like a pigeon at a wedding.
At the Cauldron, Harry's reunited with his buds Ron and Hermione. Ron's father informs Harry that Sirius Black, who just escaped from Azkaban, wants to kill Harry, and that Harry needs to be safe:
HARRY: Mr. Weasley, why would I go looking for someone who wants to kill me?
(If Mr. Weasley believes this line, he clearly hasn't seen the other two movies.)
Aboard the Hogwarts Express, Harry, Ron, and Hermione return to the greatest boarding school of all time: yup, that'd be Hogwarts.
However, the cabin air soon turns cold. The window frosts over. Evil soul-sucking beasts have come aboard. No, not Men's Rights Activists, but Dementors. These ringwraith rejects attempt to siphon Harry's soul from his body, but are stopped by Professor Remus Lupin.
When Dumbledore welcomes the student body back to Hogwarts, he informs them that the Dementors will be on Hogwarts grounds because they're searching for Sirius Black, El Chapo of the wizarding world. Professor Lupin is introduced as the new Defense Against the Dark Arts teacher. And Hagrid, our favorite gentle giant, has been promoted to teach Care of Magical Creatures.
Speaking of Magical Creatures, Hagrid introduces the students to a Hippogriff during their first class. Provoked by Draco Malfoy, Buckbeak the hippogriff injures the blonde brat, who threatens to tell his father and have Hagrid fired. And worse, poor Buckbeak is sentenced to death.
Meanwhile, Harry learns that Sirius Black isn't just a crazy killer. He was James and Lily Potter's best friend. He betrayed them to Lord Voldemort and was responsible for their deaths and the death of their friend Peter Pettigrew. Oh yeah, and he's also Harry's godfather. What's next? A hippogriff head in Harry's bed?
Harry isn't allowed to visit Hogsmeade because his permission slip wasn't signed. (Even wizards have to deal with paperwork.) The Weasley twins help Harry sneak to Hogsmeade with the assistance of the Marauder's Map, a magical piece of parchment that shows Harry the whereabouts of every person within Hogwarts walls. The Map appears to be on the fritz, though, because it shows Peter Pettigrew…even though Harry knows he is dead. Spooky.
To help Harry defend himself against Dementors, Professor Lupin teaches Harry the Patronus charm. A Patronus won't save Buckbeak, though. Harry, Ron, and Hermione watch the poor Hippogriff be executed by a man with a giant axe. Buckbeak, we hardly knew ye.
All Hades breaks loose (oh, sorry, this isn't Percy Jackson) when Ron's rat, Scabbers, escapes. Ron finds the rat near the Whomping Willow. He also finds the giant black dog that approached Harry at the beginning of the movie. The dog grabs Ron by the ankle and drags him into a tunnel at the base of the Willow. Hey, at least he didn't pee on Ron.
Harry and Hermione follow Ron inside, where they discover that the dog is Sirius Black, an Animagus. They are joined by Professor Lupin, Sirius' friend. They inform Harry that Sirius is a good guy. The person who actually betrayed the Potters was Peter Pettigrew, who is also an Animagus. Pettigrew has disguised himself as Scabbers, Ron's rat.
Snape shows up, with bad timing as always, and Harry blasts him with a disarming spell. Ouch. Considering what a jerk Snape was to Hermione earlier, Harry should have let her do it.
Anyway, Pettigrew resumes human form, still looking awfully rat like. Instead of feeding him to a life-size game of Mouse Trap, they decide to turn him in to the Dementors, which is even worse. Outside, it appears that Lupin forgot to check the moon phase on the Weather Channel that morning. The full moon appears in the sky, and Lupin, a werewolf, transforms.
As a werewolf, Lupin's unable to control himself. Or to tell friend from foe. To this giant werewolf, everyone else looks like a tasty slab of bacon on legs. Sirius shifts into a dog and fights were-Lupin to defend Harry and the gang. In the commotion, Peter Pettigrew escapes. Harry finds Sirius injured by the lake, which is swirling with Dementors. The Dementors latch onto Harry and Sirius like leeches. But someone across the pond lets out a blinding burst of Patronus, frightening the Dementors away.
Harry wakes up in the infirmary. Ron is there, recovering from being dragged half a mile by Sirius. (Why didn't Sirius just snatch the rat from his hands?) Dumbledore shows up, and tells Hermione to go back in time and fix things. He doesn't say it that bluntly of course, as the old man always speaks in riddles. (If we were in his shoes, we'd just play Cher's "If I Could Turn Back Time.")
With her Time Turner—no relation to Tina—Hermione can turn back time, and she can find a way to take back that axe that killed Buckbeak. After saving Buckbeak, Harry and Hermione wait to rescue Sirius. Harry believes his father conjured the Patronus that saved him. Hermione reminds Harry that his dad is dead, as if he forgot, but he still believes it was his father.
He's wrong. It turns out that Harry's the one that conjured the Patronus and saved himself. (Time travel makes our eyes cross, so let's not think about that one too much.) Harry and Hermione fly on Buckbeak to Hogwarts tower and break Sirius out of his little cage. He flies away on Buckbeak to fight Voldemort another day.
Harry has to say goodbye to Lupin, who has resigned…because no one wants a werewolf teaching their children. But Harry does receive some good news: a new broomstick, courtesy of his fugitive godfather. Harry flies into the Dementor-free sky, happy.
You'd be happy too if you could fly and there wasn't something lurking in the sky to suck out your soul.