Harry wakes up early on Saturday and spends hours composing a letter to Sirius that seems innocuous, but subtly mentions his scar hurting and Hagrid's absence. Harry walks up to the Owlery and sends Hedwig off. He looks out and sees one of the winged horses flying out of the Forbidden Forest. Cho enters the Owlery and quietly says that she heard about why Harry got detention. She praises his bravery. As Harry helps her secure her parcel to an owl, Filch bursts in and accuses Harry of ordering Dungbombs. He's enraged when he learns that Harry already sent his letter.
It's important to note that despite Harry's unwillingness to seek help from McGonagall or Dumbledore, he's still willing to reach out to Sirius to ask for help and information. This speaks to the intensity of their relationship and how much Harry trusts Sirius, something that will be important later on. Harry still feels this way about Sirius because, as his godfather, Sirius seems less like an authority figure and more like a friend.
Harry thinks happily about his perfectly normal conversation with Cho as he heads for breakfast. He agrees to help Ron practice Quidditch before formal practice, which makes Hermione scold them. Hermione gasps when she opens her Daily Prophet; the Ministry knows that Sirius is in London. Harry also finds another short article about Sturgis Podmore trespassing at the Ministry. Podmore is now in Azkaban. Harry remembers that Podmore was supposed to accompany them to King's Cross and never did. Ron suggests that someone is trying to frame Podmore, and Hermione thinks it could be true.
Because Harry is so happy about having spoken to Cho without embarrassing himself, he ignores the troubling fact that Filch thinks he's ordering Dungbombs and wants to see his mail. This should be a flag for Harry that someone (probably Umbridge) wants to know who Harry is talking to, likely because of his connections to the Order of the Phoenix. Umbridge won't play fair in order to get the information she wants.
Harry and Ron walk to the Quidditch pitch and Ron does surprisingly well. In the changing rooms before practice, Fred and George taunt Ron. Out on the pitch, there are Slytherins there to torment Ron even more. Pansy Parkinson insults Angelina's braids as Angelina starts a passing exercise. Ron misses several passes and then accidentally hits Katie in the face. Then they release the Bludgers and the Snitch. Angelina shouts at Ron to cover his goals and when Katie's nosebleed doesn't stop, Angelina ends practice. Hermione tries to comfort Ron, but Ron won't allow her to.
Pansy Parkinson's insult in regard to Angelina's hairstyle tells the reader that in addition to discrimination about one's blood status, the Wizarding world also suffers from racism, just like the Muggle world—insulting Angelina's braids is mocking a common black hairstyle. This allows the Slytherins’ awful nature to feel more real to readers, as this racism maps exactly onto the real world.
Ron and Harry spend all of Sunday working on their homework, and Ron wonders if Hermione would let them copy her essays. Late that night, Hermione points out several errors in Ron's essay and then points to Hermes, Percy's owl, outside the window. Ron reads Percy's letter and then disgustedly throws it at Harry and Hermione. In the letter, Percy congratulates Ron on being made a prefect, encourages Ron to distance himself from Harry and Dumbledore, and cryptically tells Ron to check the Prophet tomorrow. Harry tries to laugh, but Ron burns the letter. With a sigh, Hermione takes the boys' essays to correct them.
Percy believes that the only way forward is to get close to people with power, like Fudge. This is, notably, exactly what Umbridge is also doing as far as the reader can tell. This again expands Harry’s view of evil—it doesn’t just mean killing people or calling for blood purity, as Voldemort does. Instead, a person can be evil by trying to gain power through discrediting and harming others through legal channels.
Harry thinks that Sirius is the only person who might understand how he's feeling, and as he glances at the fire, he thinks he sees Sirius's head flash there. A moment later, Sirius's grinning head appears in the fire. He says this is the only way he can respond to Harry's letter appropriately. Sirius says he's not concerned about Harry's scar hurting and doesn't think Umbridge is a Death Eater, though she's nasty: she hates part-humans and has introduced legislation trying to control merpeople and werewolves. Sirius isn't surprised that Umbridge isn't letting students do magic; he says that Fudge is afraid that Dumbledore is forming a private army to take on the Ministry. He also says that while Hagrid is late returning from his mission, Dumbledore isn't worried.
Though Sirius makes several mistakes here in what he says to Harry, it's still important to note that unlike other adults, Sirius is at least talking to Harry, giving him information beyond what he asked for, and, for the most part, taking Harry's concerns seriously. Not acting more concerned about the pain in Harry's scar is where Sirius goes wrong here. By telling Harry it's nothing to worry about, he encourages Harry to diminish and discredit the very real and very scary things he's feeling through his scar, which again encourages Harry to go it alone.
Sirius offers to meet the trio in Hogsmeade, but all of them refuse emphatically. Harry says he wants to keep Sirius out of Azkaban, which makes Sirius say that Harry isn't as much like James as he thought. He makes an excuse to leave and then his head disappears.
Sirius's comment is a major blow for Harry, who idolizes his dad. This kind of a comment speaks to the more peer-like relationship Harry and Sirius have, as this is an inappropriate thing for a guardian to say.