School is over for the year and therefore so is 'Harry Hunting', a favourite 'sport' of Dudley's and his friends Piers, Dennis, Malcolm and Gordon. It is decided that next year Dudley will go to Uncle Vernon's old school, Smeltings. Harry will go to Stonewall High. A letter arrives for Harry in the post, but Uncle Vernon does not let him have it. The next days more letters arrive. After the letters start coming through the chimney, Uncle Vernon decides they will leave the house. The letters even arrive at the hotel they are staying in and they end up in a hut on an island.
Harry is counting down the seconds to midnight, his birthday. At exactly midnight someone bangs on the door to their hut.