Chapter 14 - "Percy and Padfoot" - In which Harry sends a letter to Sirius, he encounters Cho Chang and she calls him brave, and the Gryffindor team's first practice is less than spectacular. Percy sends Ron a letter warning him against continuing his friendship with Harry, and Sirius communicates with Harry through the common room fire.
In the Owlery
Early the next morning Harry awakens and walks down to the common room to write a letter to Sirius - which is challenging, since he must anticipate it being intercepted. He finally manages, though, and sets off to mail it.
In the Owlery, Harry mails his letter and is watching another winged horse over the Forbidden Forest when Cho Chang enters behind him. They chat for a bit, with her complimenting him for standing up to [Umbridge], when Filch arrives attempting to intercept Harry's letter. After Cho sticks up for Harry, they leave together, and Harry heads to breakfast.
An Awful Quidditch Practice
At breakfast Harry and Ron talk about [Quidditch], and Hermione learns from her [Daily Prophet] that [Sturgis Podmore] was arrested at the [Ministry of Magic]. The boys then decide to head out to the [Quidditch pitch] to practice together, despite Hermione's clear disapproval.
Harry and Ron work on their [Quidditch] skills together, then head in for a quick lunch before coming out to practice with the entire [Quidditch team]. The practice doesn't go well, though, as the Slytherins show up to heckle and Katie Bell has to be taken to the hospital wing with a bloody nose.
Hermione finally offers to correct Harry and Ron's Astronomy essays, but as she does so Harry notices Sirius's head in the fire. Sirius updates the three of them - saying he doesn't think [Umbridge] is a Death Eater, that Fudge fears [Dumbledore] is training a private army of students, and that Hagrid is fine. But when he tries to offer to meet them in [Hogsmeade], Harry refuses, at which Sirius gets upset and disappears.
Chapter 15 - "The Hogwarts High Inquisitor" - In which Umbridge is made Hogwarts High Inquisitor, and Harry loses his temper again in Defense Against the Dark Arts, serving another week's detention. Umbridge observes the professors in class, and Ron and Hermione try to convince Harry to give Defence Against the Dark Arts lessons.