Harry meets Dobby, a House-elf, when he has to stay in his room while a Uncle Vernon has a business dinner downstairs. Mr. and Mrs. Mason arrive for dinner with Uncle Vernon, Aunt Petunia and Dudley. Dobby warns Harry not to go back to Hogwarts because if Harry does, he will be in mortal danger. Harry learns that Dobby has intercepted Ron and Hermione's letters to make Harry believe he had no friends at the school. When Harry refuses to promise not to return to Hogwarts, Dobby goes downstairs to the kitchen and levitates the dessert, a cream pudding that was to be served to Dursley's guests. Then he lets it fall to the floor.
Immediately after, Uncle Vernon storms into the kitchen, raging with anger, showing him a letter which just arrived. The letter states that the Improper Use of Magic Office has found out that at 9:12 PM, in Harry's house, a Hover Charm was used, and underage wizards are not permitted to perform spells outside of school, and that further spellwork may lead to expulsion from Hogwarts. His aunt and uncle were not aware of this fact. Uncle Vernon literally locks Harry up into the house, even putting bars on Harry's window.