When the Harry Potter craze first started I really couldn't be bothered with it. Then I saw the DVD of the first film, then the second film. I got fed up waiting for film 3 that I bought the book, now I'm hooked...and the rest is history! - Here is the details from Amazon:

After just about surviving yet another summer with the dreadful Dursleys, the arrival of Aunt Marge is the final straw and, in a fit of anger, Harry casts a spell on her, causing her to blow up like a balloon. He fully expects to be expelled from Hogwarts for his blatant flaunting of the rule not to use magic outside term time, but 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.

Meanwhile Sirius Black--one-time friend of Harry's parents, implicated in their murder and follower of "You-Know-Who"--escapes from Azkaban and this has serious implications for Harry. Back at Hogwarts, Harry's movements are restricted by the presence of the Dementors--guards from Azkaban on the look-out for Black.