In this book, Harry Potter gets locked inside his home by when "he", which is actually an elf, does some magic to get him in trouble so he doesn't go to school, telling him that there is a great danger. Once at school, he starts hearing voices in his head.
Harry finds, in this book, that he isn't getting any letters from his friends. That is, until he meets the elf, Dobby, who has taken all of the letters from his friends, and is hoping to prevent Harry to going to Hogwarts saying that it is too dangerous from him. He even has him grounded by his parents to achieve this task. Eventually when Harry does get to school, he finds that many people are getting petrified. It is up to Harry to stop the person who is doing this to save his school.
Harry Potter gets driven out of his house, having accidentally done some magic to his Aunt Marge. There, he meets the Minister Of Magic himself, who surprisingly doesn't get arrested for doing magic. Instead, everyone he meets seems to be wanting to protect him from some unknown danger. Eventually, he figures out that a person who is supposed to be hunting down Harry after escaping Azkaban, the wizard prison where no one had broken except Sirius Black, a wizard who had supposedly betrayed Harry's mother and father to the darkest wizard of all time, and had killed 13 people with one curse. Can Harry really figure out the truth behind all of this madness?