The Ministry of Magic believes that Black is out to kill Harry, and that he was a friend of Harry's parents, James and Lily Potter. Believing that Black betrayed his parents to the dark wizard, Lord Voldemort, which led to their tragic death, Harry is both frightened and curious about Black's intentions.

As the year progresses, Harry learns more about his parents and their relationships with Black and other wizards. He also learns about the events leading up to his parents' death and the role that Black played.

With Ron and Hermione's help, Harry sets out to uncover the truth about Sirius Black and his connection to his parents. They learn about the Patronus Charm, a powerful spell that can drive away the soul-sucking dementors that guard Azkaban Prison.

The third year at Hogwarts School of Witchcraft and Wizardry has just begun for Harry Potter. Harry is excited to learn that he will be studying new subjects, such as Divination and Care of Magical Creatures. However, his enthusiasm is short-lived, as he soon learns that a notorious wizard named Sirius Black has escaped from Azkaban Prison.

The story begins with Harry spending the summer with his cruel and neglectful Muggle (non-magical) relatives, the Dursleys. On his eleventh birthday, Harry receives a letter from Hogwarts, and his life is forever changed.

As the year progresses, Harry learns more about Black's past and his connection to Harry's parents. With the help of his best friends Ron Weasley and Hermione Granger, Harry uncovers a surprising truth: Sirius Black is his father's best friend and is innocent of the crime for which he was imprisoned.