Chapter 1 - "Dudley Demented" - In which Harry is angry and picks on Dudley, Dudley is attacked by Dementors, and their neighbour Mrs. Figg returns.
In the Hydrangea Bush
We find [Harry] lying in the flowerbed beneath the [Dursleys]' window, listening to the news for any sign of [Voldemort]'s return as [Vernon] and [Petunia] discuss him, [Dudley], and the neighbors. Finally, Harry concludes that nothing will come of the news, and moves to leave his flowerbed.
Without warning [Harry] hears a loud crack and jumps up, smashing his head on the open window and infuriating [Uncle Vernon]. Finally, after an argument with Vernon and [Petunia], Harry insults them and walks off down the street.
A Park, a Punch, and a Patronus
[Harry] walks off alone, thinking about the crack that he heard and sure that it was the sound of someone [Apparating]. He thinks with frustration about the [Daily Prophet]'s ignorance, his lack of news from [Ron] and [Hermione], and his memories of seeing [Cedric] killed, and resists the temptation to confront [Dudley]'s gang.
Getting up from the swing, [Harry] heads for home, stopping [Dudley] en route to torment him. Dudley, however, tells Harry he's heard him crying out in his sleep, prompting Harry to threaten him with his [wand].
[Dudley] and [Harry] both feel suddenly cold and plunged into darkness, and Harry realizes that [Dementors] have appeared. Thinking it's Harry, Dudley punches him, but Harry just manages to drive them away without any permanent damage to himself or Dudley.
With the [dementors] gone, [Mrs. Figg] comes running up - and unexpectedly yells at [Harry] to keep his [wand] out.
Chapter 2 - "A Peck of Owls" - In which Harry is expelled from Hogwarts, Uncle Vernon swears, Aunt Petunia reveals knowledge of the wizarding world, Dumbledore interferes and Harry is no longer expelled, but suspended pending a Ministry of Magic disciplinary hearing.
[Mrs. Figg] reveals herself to be a [Squib] and a friend of [Dumbledore], and is furious at [Mundungus Fletcher] for shirking his guard duty responsibility. When he shows up, Mrs. Figg screams at him to run to [Dumbledore], and she manages to walk [Harry] and [Dudley] home before bolting off to her own house herself.
Harry Explains About the Dementors to the Dursleys
[Dudley] and [Harry] arrive home, where Dudley's condition causes an uproar with [Vernon] and [Petunia]. Within seconds, they call Harry into the kitchen to explain what has happened.