chapter 28 - "Snape's Worst Memory" - In which Umbridge replaces Dumbledore as Head of Hogwarts, the students (with the help of Fred's and George's inventions) rebel while the staff sit back and watch, and Umbridge tries to get Harry to tell her where Dumbledore is hiding. Harry confronts Cho about her friend Marietta, continues his Occlumency lessons with Snape, and while poking around in Snape's Pensieve discovers that his father may have been every bit as arrogant as Snape had previously told him.
A New Headmistress and an Inquisitorial Squad
Morning dawns with news that [Umbridge] has replaced [Dumbledore] as [headmaster]. Students talk about what happened the previous night with Dumbledore's escape, and about how Umbridge can't get into [Dumbledore's office].
Draco Malfoy interrupts Hermione's comment about [Umbridge], and the group soon learns that he's a member of the newly formed Inquisitorial Squad, which has the hpower to dock [points]. He briefly abuses his power before sauntering off laughing, and the group turns around to see the points indeed being taken away.
Fred and George arrive as Malfoy departs, admit that they've stuffed [Montague] in a [Vanishing Cabinet], and warn everyone else to be in the [Great Hall] for lunch, so as to not get blamed for the bit of mayhem that's been planned.
Filch unexpectedly brings Harry to [Umbridge]'s office, where she attempts to slip him [Veritaserum] and interrogates him about the whereabouts of [Dumbledore] and of Sirius Black, though Harry admits nothing. They're interrupted by a loud bang, however, and they both go rushing out of the office.
Harry leaves [Umbridge's office] to find fireworks exploding up and down the highway, and laughs as [Umbridge] tries to [Stun] them and they instead double in size. Harry ducks through a door to find Fred and George celebrating their achievement, and over the rest of the day the teachers refuse to do anything about the fireworks, instead letting Umbridge run around like crazy.
Dreaming, Harry again gets further than ever into the [Department of Mysteries], but is awakened by a loud bang from one of Fred and George's [fireworks]. He then lies, feeling frustrated both that he didn't get further and that he hasn't been able to practice [Occlumency].
Harry Sees More than he Should
As Snape prepares to begin Harry's [Occlumency] lesson, Malfoy bursts in with news that [Montague] has turned up. Snape rushes out, with orders to Harry to resume the lesson the following evening, and Harry turns to go as well when he spots something out of the corner of his eye - Snape's [Pensieve]. Recklessly, he dives inside.