Chapter 14 - "Snape's Grudge" - In which security is tightened, Hagrid is summoned to London with Buckbeak, Ron and Harry plan another visit to Hogsmeade despite Hermione's appeals, Harry wears his invisibility cloak and while playing a trick on Malfoy and his goons is unmasked, rushing back to school only to be confronted by Snape, questioned and only saved by the arrival of Lupin.
Sir Cadogan is Fired
[Harry] is awakened suddenly by a scream, which he realizes came from [Ron] - he soon learns that Ron has seen [Sirius Black] standing over him with a knife, and they all run down to the common room, where Ron tells everbody what he's seen.
[Professor McGonagall] reappears amidst the noise, but when she's told by [Ron] that [Sirius Black] was in his [dormitory] - and [Sir Cadogan] confirms it - she is stunned, and soon learns that [Neville] was responsible for losing the passwords.
Upon receiving the news that [Sirius Black] has escaped again, security around the castle tightens, including the [Fat Lady]'s returning to guard [Gryffindor Tower] once again. [Harry] and [Ron] wonder momentarily about telling someone about the one-eyed witch passageway to [Honeydukes], but decide against it.
In the days following [Sirius Black]'s near-attack, [Ron] becomes a celebrity and [Neville] is completely disgraced, even receiving a [Howler] from his [Gran] for losing the [Gryffindor Tower] passwords.
Hagrid Teaches the Meaning of Friendship
[Harry] and [Ron], at breakfast, receive a note from [Hagrid] inviting them to tea that afternoon.
As per their invite, [Harry] and [Ron] head down to [Hagrid]'s to visit - where they realize they've forgotten to work on [Buckbeak]'s appeal, and get a stern lecture about their treatment of [Hermione], before Hagrid walks them back up to the castle.
Draco Gets a Faceful
When they learn about an upcoming trip to [Hogsmeade], [Harry] and [Ron] begin plotting to go when [Hermione] threatens to tell a teacher. [Ron] cruelly pretends to ignore her and she runs away upset, and Harry decides to go, but with his [Invisibility Cloak].
Trying to get to [Hogsmeade], [Harry] instead encounters [Neville] and then [Snape], delaying him before he finally makes it out of the castle.
After running to [Hogsmeade], [Harry] finally meets up with [Ron] and Ron gives him a tour, ending at the [Shrieking Shack]. When [Malfoy] and his cronies arrive, Harry, invisible, slings mud at them and trips them - until the [Invisibility Cloak] comes off and reveals his head. [Malfoy] runs back to school to tell the teachers, and Harry quickly realizes that he'd better hurry back as well.