Forced to do his homework in the dead of night and forbidden to refer to his magic skills or his life at Hogwarts school, Harry Potter is forced to endure the summer holidays with the dreaded Dursleys. The arrival of Aunt Marge is the final straw and, in a fit of anger, Harry breaks all the rules and casts a spell on her, causing her to blow up like a balloon. Running away from his dreaded relatives, Harry expects to be expelled from Hogwarts for his blatant flaunting of the rule not to use magic outside term time. However, the arrival of the mysterious Knight Bus and a meeting with Cornelius Fudge, the Minister of Magic, result in Harry enjoying the rest of the holidays in the wonderful surroundings of the Leaky Cauldron.
The escape of Sirius Black--one time friend of Harry's parents, implicated in their murder and follower of "You- Know-Who"--from Azkaban, has serious implications for Harry for it would appear that Black is bent on revenge against Harry for thwarting "You-Know-Who". Back at Hogwarts, Harry's movements are restricted by the presence of the Dementors--guards from Azkaban on the look out for Black--however, this doesn't stop him throwing himself into the new Quidditch season and going about his normal business--or at least attempting to. Despite warnings Harry is determined to get to the bottom of the mystery surrounding Sirius Black--how could this one-time close friend of his parents become the cause of their deaths?
And why does the presence of the Dementors have such a devastating effect on him, causing him to hear the last moments of his mother's life?