Harry Potter and the Prisoner of Azkaban

Contrary to everything we've been led to believe, Sirius Black (Gary Oldman), the escaped "Prisoner of Azkaban" of the title is not:

Sirius Black, however, is:

In the end, Black is able to prove his innocence to Harry, Ron, Hermione (Emma Watson) and the new Defense Against the Dark Arts teacher, Professor Lupin (David Thewlis). Together they capture Pettigrew, and though Black wants to kill Pettigrew, Harry convinces him to turn Pettigrew over to the Dementors. Snape (Alan Rickman) tries to interfere, but our heroes win out. Unfortunately, as the crew is bringing Pettigrew to justice, Lupin makes his monthly transformation into a werewolf. In the confusiuon, Pettigrew transforms into a rat again, and escapes. Black is then captured, and prepared to have his soul sucked out by the Dementors. Dumbledore (Michael Gambon) believes the kids' story, so he convinces Harry and Hermione to use Hermione's secret time-travel device (which she carries around in order to take multiple classes simultaneously) to liberate Black and the also-condemned-to-death Hippogryph, Buckbeak. Black makes good his escape, but is still a fugitive.