Chapter 8 - "The Deathday Party" - In which Harry is caught dripping mud on the carpet by Filch, is taken to Filch's office, discovers that Filch is not a wizard, and Nearly Headless Nick invites him to his Deathday Party, which HRH attend on Hallowe'en night. Leaving the party, Harry hears voices again, and following the sound with Ron and Hermione discovers writing on the wall and a Petrified Mrs. Norris.

Detention with Lockhart
Back in the [entrance hall], Harry and Ron run into Professor McGonagall, who informs them that their detentions will be that evening - and that Harry will be spending his with Lockhart.
With Ron gone off to the trophy room with Filch, Harry reluctantly heads for Lockhart's office. There he helps Lockhart answer his fan mail, and for the first time hears a venemous voice in the walls.
After waiting for Ron to return from detention, Harry tells him about hearing the voice while he was in Lockhart's office, but they can't figure it out.
As October arrives and passes, a spate of colds flows through the school, leading Madam Pomfrey to hand around [Pepperup Potion]; meanwhile, [Oliver Wood] continues to lead the [Gryffindor Quidditch team] through manic practices.
Conversations with Nick and Filch
Returning muddy from a tough [Quidditch] practice, Harry runs into Nearly Headless Nick, who shares his disappointment at being rejected by the [Headless Hunt]. Soon, though, Filch arrives, screaming at Harry for dragging mud through the [entrance hall].
Filch drags Harry off to his office, but is distracted by a large bang overhead. When he leaves, Harry discovers a Kwikspell envelope on Filch's desk - and when Filch returns he notices it's moved and kicks Harry out of his office.
Amazed at his luck in escaping punishment, Harry runs from Filch's office and again runs into Nearly Headless Nick. Nick then invites Harry to his [Deathday Party, and Harry agrees to go.
Harry tells Hermione and Ron about Nick's [Deathday Party], and they agree to go, as the three of them sit watching a salamander ricocheting around the common room.
The Deathday Party and What Came After
On Halloween, Harry, Ron, and Hermione head to Nearly Headless Nick's [Deathday Party], where they chat with Peeves and Moaning Myrtle, avoid the foul food and watch the [Headless Hunt] before heading back to try to catch the end of the Halloween feast.