In "Harry Potter and the Prisoner of Azkaban," the third book in the Harry Potter series by J.K. Rowling, young wizard Harry Potter returns to Hogwarts School of Witchcraft and Wizardry for his third year. He learns about the escaped prisoner Sirius Black, who is believed to be after him. As Harry navigates new classes and friendships, he discovers more about his past and the truth about his family. Throughout the year, Harry, along with his friends Hermione Granger and Ron Weasley, encounters magical creatures and learns about the Dementors, dark creatures that guard Azkaban. The story explores themes of friendship, loyalty, and the complexities of good and evil, culminating in a surprising revelation about Sirius Black and his connection to Harry.