Harry Potter and the Prisoner of Azkaban by J. K. Rowling

Harry Potter is lucky to reach the age of thirteen, since he has already survived the murderous attacks of the feared Dark Lord on more than one occasion. But his hopes for a quiet term concentrating on Quidditch are dashed when a maniacal mass-murderer escapes from Azkaban, pursued by the soul-sucking Dementors who guard the prison. It’s assumed that Hogwarts is the safest place for Harry to be. But is it a coincidence that he can feel eyes watching him in the dark, and should he be taking Professor Trelawney’s ghoulish predictions seriously?