Chapter 13 - "Detention With Dolores" - In which Hermione stops the twins from experimenting on first-years, Ron tries to stop unknowing house-elves from taking Hermione's knitted hats, and Professor Grubbly-Plank teaches Care of Magical Creatures as there is still no sign of Hagrid. Harry serves Umbridge's detentions, in which an enchanted quill cuts lines into the back of his hand, and Ron tries out for and makes the Gryffindor team as Keeper.

An Awful Monday
Departing Potions, Ron and Hermione begin arguing over whose side Snape might be on, when Harry suddenly yells at them for their bickering and storms off, spending lunch hour sitting at the base of the North Tower.
Ron arrives to Divination with the news that he and Hermione have decided to stop arguing, but that they also think Harry's treating them unfairly. Soon, however, class begins, with boring work of trying to interpret dreams, not to mention a load of homework.
[Umbridge]'s first Defence Against the Dark Arts class begins with silent reading, but soon Hermione questions the idea that the class won't be using any spells, leading to a class uproar. It finally culminates in a showdown between Harry, who stands by his conviction that Lord Voldemort has returned, and Umbridge, who blatantly calls him a liar. She finally hands Harry a note for McGonagall and orders him out of the room.
Storming from class, Harry runs past Peeves and into McGonagall, who brings him into her office. Upon learning of his behavior in [Umbridge]'s class, she warns Harry of what his behavior around Umbridge could cost him, and sends him away.
Sitting at dinner, Harry gets more and more frustrated as he hears students around the Great Hall gossiping about him, and finally he, Hermione, and Ron walk out in frustration.
While Doing Homework in the Gryffindor Common Room
Hermione explains to Harry why student aren't believing him or [Dumbledore] as they and Ron walk back to the common room together. After venting their frustration at [Umbridge]'s hiring, they settle in to do some homework.
Hermione looks up from her homework and spots Fred and George with some first years, testing their products. She marches up to them and demands they stop, threatening to tell Mrs. Weasley if it continues.
On her way up to bed, Hermione puts out some hats she's knitted for house-elves, in the hopes that they will find them and be set free. Harry and Ron finally give up on their homework, then, and go to bed themselves.
More Classes and Welcome Support
The second day of classes piles more work on Harry, Ron, and Hermione, with both Flitwick and McGonagall giving the fifth years lectures on the importance of [O.W.L.s], and Harry and Ron spend their lunch hour in the library focused on work.