Harry’s third year at Hogwarts is stressful in the beginning. He is constantly being buried under piles of homework. He also learns that Sirius Black, a mass murderer, is out to kill Harry. Mr. Weasley makes Harry promise that he won’t go looking for Sirius and Harry agrees. At Hogwarts, Dementors have been stationed around the school to prevent Sirius from getting in. The Dementors, however, have a worse effect on Harry than any other student because of Harry’s past. Mr. Lupin, the new Defense Against the Dark Arts teacher, teaches Harry how to cast a Patronus Charm which is the only spell that works against the Dementors. Ron and Hermione are constantly arguing because Hermione’s cat keeps trying to eat Ron’s rat. Soon they altogether stop talking because Ron thinks that Hermione’s cat did eat his rat. A few days later Sirius Black breaks into Hogwarts, but is quickly captured. Then as it turns out, Ron’s rat is not only alive, but a real human that transformed himself into a rat to spy on Harry. The man’s name is Peter Pettigrew and he was spying on Harry for Voldemort. Pettigrew quickly escapes before Harry can stop him. Harry finds out that it wasn’t Sirius Black that lead Voldemort to his parents, but that it was Pettigrew. Sirius is actually Harry’s godfather. Harry hopes that he can live with Sirius instead of the Dursley’s, but Sirius has to hide from the Ministry. Professor Lupin turns out to be a werewolf, and it was Sirius that saved the kids from Lupin.