Harry Potter and the Prisoner of Azkaban

Harry, Ron and Hermione return as teenagers for a third term at Hogwarts School of Witchcraft and Wizardry. But Harry's fate, and that of the entire community of wizards, looks bleak when the infamous Sirius Black--convicted of abetting evil Lord Voldemort by killing 13 people with a single curse--escapes from prison. The only clue to where Sirius is headed: The Azkaban guards heard Black muttering in his sleep "He's at Hogwarts ... He's at Hogwarts." Now, even within the walls of his magical school, Harry may not be safe from a convicted killer in Harry Potter and the Prisoner of Azkaban.