One day, Uncle Vernon tells Harry to get the mail. Harry does as he's told, and is extremely surprised that there is a letter addressed to him. It said: To Mr. Harry Potter, 4, Privet Drive, The Cupboard Under the Stairs.
He starts opening it, but Dudley shouted, "Hey, look! Harry's got a letter!" Uncle Vernon couldn't believe Harry actually got a letter. After reading it, he was in shock. He forbid Harry to read it, and moved him to Dudley's old bedroom, because the thought that whoever wrote the letter knew that Harry sleeps in the cupboard was unnerving.
The next day, another letter came, this time, it said "the smallest bedroom." Uncle Vernon was a little worried, because he knew someone was watching them. Uncle Vernon still keeps Harry from reading the letter.
The next morning, Harry gets up early because he really wants to read the letter, but Uncle Vernon, who slept by the mail slot, stopped him.
Later, the letters flood the house, but Harry still doesn't get to read them. Uncle Vernon decides to move somewhere else, hoping the person that keeps sending the letters still lose track of where they are.
They went to a hotel, and 100 letters addressed to Harry arrive there. On a dark stormy night, the family is out on an island in the middle of nowhere. This time, Uncle Vernon is sure no one can find them here. They put up a tent and bolt the door.
It happens to be Harry's birthday. At midnight, they hear a thump on the door.