Harry Potter and the Prisoner of Azkaban attacked by a big black dog, which Harry has seen several times before. The dog drags Ron through a tunnel under the Whomping Willow into the Shrieking Shack. Harry and Hermione follow, and there is a brief standoff when they find Ron with Sirius Black, who has transformed from the dog. Lupin enters, and they explain the situation to Harry and his friends: Lupin is a werewolf, which led to his friends James Potter, Sirius Black, and Peter Pettigrew becoming animagi. Lupin explains that Scabbers is Pettigrew in his animal form; he has been hiding from Black, whom he had
Harry Potter diary into Hogwarts. The third novel, "Harry Potter and the Prisoner of Azkaban", follows Harry in his third year of magical education. It is the only book in the series which does not feature Lord Voldemort in any form. Instead, Harry must deal with the knowledge that he has been targeted by Sirius Black, his father's best friend, and, according to the Wizarding World, an escaped mass murderer who assisted in the murder of Harry's parents. As Harry struggles with his reaction to the dementors – dark creatures with the power to devour a human soul and feed on despair