This is the Third book in the Harry Potter series. This is Harry's third year at Hogwarts, and the year starts off with an escape from prison, by the person who was convicted of turning Harry's parents over to Voldemort, though Harry has no idea who he is or what he has done. Harry returns to school, and many things happen, the school is being guarded by Dementor's the guards from Azkaban. Also, Harry and his friends start new classes, and have another new teacher for Defense Against the Dark Arts. Harry has a very busy year, with studying, and Quiddich, plus everything else that his happening at school.
Very good, I really enjoy these books, and this is one of the best, actually, I think as they progress, they get better.