Lupin and Sirius explain that Sirius is actually innocent and that they were friends with Harry's parents. They reveal that the person who actually betrayed Harry's parents was a man named Peter Pettigrew. Sirius and Lupin then use magic to reveal that Ron's rat is actually Peter Pettigrew. Peter escapes and Sirius is caught by the Dementors. The headmaster, Professor Dumbledore, helps Harry and Hermione use time travel to save Sirius from the Dementors. Professor Lupin resigns from his job because he is actually a werewolf.