As Harry runs back through the tunnel to Hogwarts, he wonders why nobody told him that his parents died because their best friend betrayed them. Hermione and Ron keep a nervous eye on Harry until after dinner, when Harry excuses himself early to go to bed. He digs in his cabinet until he finds the photo album that Hagrid made him. Harry finds a photo of Lily and James's wedding and notices Black as their best man. Harry thinks that Black doesn't have to hear Lily screaming whenever the dementors get close, slams the album closed, and crawls into bed. When Ron comes up moments later, Harry pretends to be asleep. Harry lies awake for hours, feeling as though his anger at Black is like poison.
To the reader, it makes more sense that nobody told Harry the "truth" about Black because they knew he'd react this way. He and Ron already have a reputation for getting into trouble, and chasing after an escaped criminal sounds exactly like something they'd try to do. This shows that the adults in Harry's life understand how to filter what he hears and control his perspective to try to keep him safe from harm.
Harry wakes up close to lunchtime the next day and finds Ron and Hermione in the common room. Hermione tells Harry that no matter what he heard, he can't do anything stupid. Incensed, Harry tells them that he hears Lily screaming when the dementors get near, and now that he knows who's responsible, he wants revenge. Hermione looks panicked as Harry says that Malfoy has known about this all along, but Ron points out that Malfoy would love it if Harry got destroyed like Pettigrew.
Ron and Hermione's choice to confront Harry about his anger shows that, like the adults around them, they're also aware that Harry is prone to following his emotions instead of logic or the promise of safety. This shows that, in this way, they're capable of behaving more maturely than he is, if only because their emotions aren't quite so high.
Ron tries to change the subject by suggesting they go visit Hagrid and Harry jumps at the idea, as he can ask Hagrid why he never mentioned Black. Hagrid doesn't answer when they knock and Ron hears a strange noise inside. When they call for Hagrid he finally opens the door in tears and flings himself at Harry. Harry, Ron, and Hermione guide Hagrid to a chair, and Hagrid motions towards an official letter on the table. Harry reads it aloud; it's from the school governors, who have decided to refer Hagrid and Buckbeak's case to the Committee for the Disposal of Dangerous Creatures. Ron insists that Buckbeak will get off and Harry notices that Buckbeak is inside.
Ron's remark that Buckbeak is innocent shows that he still trusts that, with proper preparation and witness testimony, Buckbeak can win his case. This represents a belief in the goodness and righteousness of the Ministry of Magic that they'll soon realize is unfounded: the Committee for the Disposal of Dangerous Creatures is controlled by Lucius Malfoy, and it cares little for the facts of the case.
Hermione says that they should be able to put up a good defense, but Hagrid cries that the Committee members are Lucius Malfoy's cronies and Dumbledore is too busy to help. Harry can't bring himself to mention Black, so he suggests that he can help Hagrid prepare for the case. After Ron makes tea, Hagrid starts to calm down, though he says that nobody likes his classes and the dementors make him feel terrible. This is the first time Hagrid has ever spoken about his time in Azkaban. When Hermione points out that Hagrid was innocent, he says that the dementors don't care.
Again, Hermione's insistence that they can win the case if only they prepare is predicated on a belief that the justice system is fair and unbiased—which, given that Lucius Malfoy controls this committee, it's clearly not. Hagrid's comment about the dementors mirrors this, given that the dementors also don't care about innocence—they'll suck the life out of anyone, innocent or otherwise.
After their visit, Harry, Ron, and Hermione devote themselves to helping Hagrid prepare for the hearing. They work almost nonstop until Christmas, when Harry and Ron wake to find sweaters and sweets from Mrs. Weasley. Harry also has a long, thin package and opens it to discover a Firebolt. There's no card and the boys wonder who sent it. Hermione arrives with Crookshanks and when she learns that the broom came without a note, she's not excited. Before she and Ron can argue, Crookshanks leaps at Ron and Scabbers. Ron tries to kick at Crookshanks but kicks Harry's trunk instead, which reinvigorates the Pocket Sneakoscope. Hermione huffs out of the room while Harry puts the Sneakoscope away.
When the Sneakoscope goes off again, it's doing so because of Scabbers. Ron's insistence that Scabbers is a victim, however, keeps him from being willing to question who around him might be untrustworthy. This reminds the reader that, because the trio doesn't have enough information to make truly informed decisions and assessments, they're missing clues right and left that could lead them towards a better understanding of the events taking place around them.
Harry notices that Scabbers looks awful and thinks that he's likely not going live much longer. Hermione and Ron refuse to speak to each other all day. When they go to the Great Hall for lunch, they discover a single table in the middle of the room for the few teachers and students still at school for Christmas. Dumbledore greets everyone warmly, makes Snape hold one end of his Christmas cracker, and puts on the ridiculous hat that comes out of it. Harry and Ron smile when they see that the hat has a vulture on it, just like the hat that boggart Snape wore.
Hermione and Ron's tiff still looks childish and silly, which reminds the reader that the trio still has a long ways to go in their journey toward maturity. When Dumbledore makes Snape participate in the Christmas cracker, he attempts to humanize Snape for the students in attendance and show them a side of Snape they wouldn't otherwise see.
As the group begins to eat, Trelawney comes into the Great Hall. Dumbledore draws up a chair for her, but Trelawney refuses to sit down since she'd be the thirteenth guest. With McGonagall's prodding, Trelawney finally sits, looking as though she expects something to go wrong. She and McGonagall heatedly discuss Lupin's absence and Trelawney's "inner eye," but Dumbledore stops them by saying that Lupin is ill again. He confirms that Snape made Lupin his potion and then offers a first-year boy a plate of sausages.
The fact that Dumbledore knows about the potion that Snape is making for Lupin should tell Harry, Ron, and Hermione that there's nothing nefarious going on—they trust Dumbledore, and Dumbledore has encouraged them in the past to trust him about Snape and his other hiring decisions.
Two hours later, Ron and Harry get up from the table at the same time. Trelawney shrieks and asks who stood up first, but McGonagall drily says that the boys will be fine unless there's a murderer in the hallway. Hermione stays behind as Harry and Ron head back to the common room to admire the Firebolt. A few minutes later, Hermione and McGonagall both come through the portrait hole. McGonagall takes the broom and tells Harry that she has to confiscate it to test it for jinxes. Ron and Harry are aghast, but McGonagall carries the broom away. Ron turns on Hermione and asks why she told. Hermione defiantly says that she believes that Sirius Black sent the broomstick.
Hermione's actions should be commended here, as she acted to make sure that Harry stayed safe at a time when most people believe that Harry isn't safe at all. She knew that Harry and Ron would be upset with her, but she acted anyway. Per the novel's portrayal of friendship, this is one of the most powerful things friends can do for one another, and it's a mark of maturity for Hermione that she did this. On the other hand, Harry and Ron's anger looks shockingly immature in comparison.