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.
Hagrid Teaches the Meaning of Friendship
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.
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.