Harry Potter and the Prisoner of Azkaban is the third novel in the Harry Potter series written by J. K. Rowling. The book was published on 8 July 1999. The novel won the 1999 Whitbread Children's Book Award, the Bram Stoker Award,and many more.

This book talks about mostly Sirius Black, his escaped, and his attempts to reach out Harry, explaining the truth. But on the other hand, Harry believes that Black is trying to kill him, he believes that Black is a convicted murderer. At that time Dementors are scattered, looking for Black and Harry has difficulties dealing with Dementors, luckily he has his new Defense Against dark arts teacher, Professor Lupin, who teaches him how to repel Dementors. Later he overheard minister Fudge talking to some of the teachers about Black, he mentioned that Black is actually a close friend of Harry's parents, however, he betrayed them, by giving Voldemort access to Potter's house and he also killed 13 Muggles and his friend Peter Pettigrew.

However, all of those stories are all wrong, when one day, Ron's rat, Scabbers disappears and suddenly a big black dog appears, dragging Ron through a tunnel under the Whomping Willow into the Shrieking Shack and it was later known to be Sirius. Inside the Shrieking Shack, Sirius explains everything, and Lupin happens to be there too. Sirius explains that Ron's rat, Scabbers is Peter Pettigrew and Lupin is a werewolf. Peter was the one who betrayed the Potters. Both 4 of them were best friends since Hogwarts, and in order to help Lupin, they used animagi spell, becoming animal.