Harry leaves [Uncle Vernon] and rushes back upstairs excited, though not before making fun of [Dudley] on the way. There he finds a letter from Ron, also inviting him to the [Quidditch World Cup]. He writes back to Ron saying he can go and finishes penning his letter to Sirius, then sits and thinks over his excitement while enjoying a piece of birthday cake.
Chapter 4 - "Back to the Burrow" - In which Harry awaits the arrival of the Weasleys, who arrive by Floo powder and must blast their way out of the blocked-off fireplace. The twins drop some toffees, then Floo back to the Burrow with Harry's trunk. Just as Harry is about to leave, Dudley eats one of the toffees and grows a huge purple tongue. Harry leaves Mr. Weasley to sort it out as Uncle Vernon begins throwing ornaments.
Despite being late, the Weasleys do arrive - but they attempt to arrive by [Floo] and get stuck inside the [Dursleys]' false fireplace. Finally, Arthur blows it out, and Ron, Harry, and the [twins] bid good-bye to the Dursleys. As they are leaving, though, [Dudley] eats one of the twins' candies that Fred "accidentally" dropped, making his tongue swell to several times its normal size, and Arthur is sorting the whole thing out as Harry regretfully departs.
Chapter 5 - "Weasleys' Wizard Wheezes" - In which the Weasleys return home, Fred and George are reprimanded by Mr. and Mrs. Weasley for giving Dudley the toffee, we learn more about the Weasley clan, and they have dinner in the garden.
Mr. Weasley Yells at Fred and George
When Mr. Weasley arrives he begins yelling at Fred and George for giving [Dudley] a [ton-tongue toffee]. However, to his surprise, Mrs. Weasley soon walks in, inquiring as well. Ron and Harry make a quick exit with Ginny and Hermione, just before Mr. Weasley breaks the news to his wife.
Percy's New Job
Up in Ron's room, he, Ginny, and Hermione update Harry on Ron's new owl, Pigwidgeon, and Percy's love of his job and his boss, [Mr. Crouch]. Ron also begins to ask about Sirius but catches himself when he realizes Ginny is present, and to cover the silence Hermione suggests they return downstairs.