Harry is miserable about the conversation he overheard, and dangerously angry at Sirius Black. Ron and Hermione try to talk him out of doing anything risky, such as pursuing Black for revenge, and as a change of topic and scenery, they decide to visit Hagrid. The visit is not a happy one, as Hagrid has just received note that Buckbeak, the hippogriff that attacked the Malfoy, is going to be put to trial in April and potentially executed. Harry, Ron, and Hermione comfort Hagrid and then head back to the library to research historical cases in which magical creatures won trials. They find nothing hopeful.
On Christmas day, Harry wakes up to find a Firebolt broomstick in his pile of presents. Although there is no card, he is thrilled. Hermione is wary, and after the Christmas dinner, during which Professor Trelawney predicts several more deaths, Hermione reports the broomstick to Professor McGonagall, who comes into the common room that night to take it away for examination, in case it had been sent by Sirius Black. Ron and Harry are furious at Hermione.
Classes resume, and Oliver Wood promises to persuade Professor McGonagall to give back Harry's Firebolt. In the meantime, Harry begins meeting weekly with Lupin to practice the anti-Dementor spell, which is intended to conjure up a Patronus, a silvery protective charm. Lupin tells Harry to focus on his happiest thought before saying "Expecto Patronum" and repelling the Dementor, or in this case, a Boggart that takes the shape of a Dementor around Harry. Harry tries this complicated spell several times with varying happy thoughts—flying on a broomstick, winning the House Championship, and leaving Privet Drive for Hogwarts. The last thought brings him some success, but he is still weak after the encounter. Each time the lesson ends, Lupin gives him chocolate and sends him on his way. Harry senses, however, that one reason he is unable to conjure a proper Patronus is that he secretly does not want to do away with hearing his parents' voices ever again.
Time moves on, and Hermione is still overworked with classes; Oliver Wood returns defeated from his visit with Professor McGonagall, who refused to give back the broomstick yet. During another lesson with Lupin, Harry inquires what is below a Dementor's cloak. Lupin answers that the only people who truly know are not in the state to report it, as the Dementor will only lower its cloak when it is preparing to administer the "kiss," which essentially sucks the soul out of the person who is kissed. Lupin adds that the Ministry of Magic has given the Dementors permission to administer the kiss to Black if they find him. Harry is a bit shaken by these thoughts as he leaves, and runs into Professor McGonagall, who returns to him the Firebolt. That night, the Gryffindor common room is alight with astonishment at Harry's broomstick, and even Hermione looks up from her books to talk with Harry. All is well, until Ron returns from his dormitory to report furiously that Scabbers is missing, that his sheets are slightly bloodied and strewn with orange cat hairs.
The Firebolt broomstick instance is folkloric; in adventure myths, the hero is often given a magical gift that helps him on his way. In the first book, Harry is given an invisibility cloak, and in the second, he is given what appears to be help through his discovery of an old diary floating in the toilet. Here, Harry receives a replacement broomstick, an anonymous gift that plays on this ambiguity of a magical bit of help that may not turn out to be what it seems; out of fear that it is a gift form Sirius, Hermione turns the broom in. In the end, she is correct about the giver, but not about the danger.
The unjust conviction of Buckbeak foreshadows Harry's hatred toward Black. Malfoy frames Buckbeak just as Peter Pettigrew frames Black in a later chapter. This incident shows us reverse sides of a legal system that is attacking an innocent beast and has lost track of the murderer of Harry's parents. These two situations are both unfair but in vastly different ways. Furthermore, the sentiment Harry feels now toward liberating Buckbeak returns once he discovers Black's innocence. Another false conviction occurs at the end of Chapter Twelve. When Scabbers has disappeared, blood appears on Ron's sheets, and cat hairs linger near the site of the crime. The lesson learned in the many mistakes Professor Trelawney makes in her predictions is reinforced by these occurrences—things are not always what they seem, and thus the future is very difficult to predict.
Learning more about the Dementors and how to fight them is the continuation of Harry's new stage of magical agency, beginning with his flight from the Dursleys, moving through his willingness to confide in Professor Lupin, and now landing him in these lessons, where he works hard each week to learn how to confront his greatest personal demon. The presence of his parents' voices in his bouts of Dementor "depression" is significant, and to be expected. Harry is constantly aware of his loss of them, and although he never knew his parents, he believes in their love for him, and he battles Voldemort and his servants, in part to protect himself, and in part to avenge their deaths.