[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.
With [Harry] packed and ready to go, he and the [Dursleys] wait nervously for the [Weasleys]' arrival.
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
[Harry] speeds through the [Floo] to the [Burrow], where he finds [Fred and George] along with [Ron], [Bill], and [Charlie], and tells them about [Dudley] eating the [ton-tongue toffee].
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.
[Ron] and [Ginny] explain to [Harry] about [Fred and George]'s new attempt at a business, [Weasleys' Wizard Wheezes], and [Mrs. Weasley's] frustration over it.
Percy's New Job
Partway up the stairs, [Harry], [Ron], [Hermione], and [Ginny] are stopped by [Percy], who complains about their racket as he's working on a report on [cauldrons] for the [Ministry of Magic].
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.