哈利波特十分不情愿的在姨妈家里度暑假，得不到魔法界的一切消息，罗恩和赫敏的信便成了他的**安慰。玛姬姑妈前来探望哈利的姨夫，哈利因为受不了她对哈利父母的污蔑，把玛姬姑妈变成了一个胀大的气球。害怕受到惩罚的哈利逃进夜幕，于是开始了新的冒险。

慌乱中哈利看到一条黑色的大狗，而在魔法界这是死亡的象征。在回学校的火车上，哈利见识到了传说中的摄魂怪，许多可怕的感觉包围着他。学校里哈利又看到了那条象征死亡的大狗，此时哈利也知道了他父母的死因，一切都归罪于小天狼星布莱克。哈利决定报仇。

卢平教授传授哈利抵制摄魂怪的魔法，在活点地图的帮助下，哈利终于在尖叫棚屋里找到了小天狼星。小天狼星用魔杖直指罗恩的宠物斑斑，随着斑斑化成人形，小天狼星讲述了事情的真相，眼看小天狼星要恢复清白，斯内普破坏了这一切。

小天狼星被捕了，哈利不忍自己的教父受摄魂怪的折磨，在校长邓布利多的指导下帮助小天狼星逃脱。

Ｆor twelve long years, the dread fortress of Azkaban held an infamous prisoner named Sirius Black. Convicted of killing thirteen people with a single curse, he was said to be the heir apparent to the Dark Lord, Voldemort.
Now he has escaped, leaving only two clues as to where he might be headed: Harry Potter's defeat of You-Know-Who was Black's downfall as well. And the Azkaban guards heard Black muttering in his sleep, "He's at Hogwarts... he's at Hogwarts."
Harry Potter isn't safe, not even within the walls of his magical school, surrounded by his friends. Because on top of it all, there may well be a traitor in their midst.