Harry Potter and the Prisoner of Azkaban

Sirius Black breaks out of Azkaban, and everyone says he's out to kill Harry. Dementors guard Hogwarts, and new teacher Lupin teaches Harry to fight them off with a Patronus. In the end, the trio learns the truth in the Shrieking Shack: Sirius is innocent and Harry's godfather, Lupin is a werewolf, and the traitor who sold out Harry's parents was Peter Pettigrew, hiding for years as Scabbers, Ron's rat. Pettigrew escapes when Lupin transforms. Sirius is caught, but Harry and Hermione use a Time-Turner to go back a few hours, save Buckbeak the hippogriff and help Sirius flee. Lupin resigns, and Harry gets a Firebolt from his godfather. Left open: Pettigrew is free, and Trelawney predicted that Voldemort's servant would return.

1. ChangeThe film never explains the Marauders

   In the book, Lupin and Sirius explain who Moony, Wormtail, Padfoot and Prongs were and how they made the Marauder's Map. The film uses the nicknames but never explains where the map came from.

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2. ChangeThe Firebolt shows up much earlier

   In the book, Harry gets the Firebolt at Christmas and McGonagall confiscates it to have it checked. In the film it only appears in the final scene.

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3. ChangeGryffindor wins the Quidditch Cup

   The book has three matches and ends with Gryffindor winning the Quidditch Cup. The film shows a single game and leaves the final out.

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4. ChangeSir Cadogan stayed in the editing room

   In the book, the portrait knight Sir Cadogan guards Gryffindor Tower in place of the Fat Lady. Paul Whitehouse filmed the part, but almost all of it was cut.

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5. ChangeCrookshanks and Sirius, real friends

   In the book, Hermione's cat realizes the black dog isn't an ordinary dog and helps Sirius. The film drops that friendship.

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