Animosity between Ron and Hermione has reached an all-time high, after the apparent death of Scabbers at the claws of Crookshanks. To cheer Ron up, Harry offers him a ride on the new Firebolt after Quidditch practice, and Ron happily accepts. The Gryffindor team is busily preparing for the game against Ravenclaw. As Harry's confidence on the new broomstick soars, the rest of the team's confidence rises as well, and the game prospects seem grand. Everybody, especially Oliver Wood, and even Percy Weasley and his girlfriend Penelope, is excited about the coming game. When the players mount their broomsticks and begin the game, the announcer, Lee Jordan, is so focused on Harry's new broomstick that he forgets to comment on many of the basic plays between the teams. Harry is playing seeker against Cho Chang, a pretty and athletic Ravenclaw fourth-year girl on whom Harry seems to be developing somewhat of a crush. Once, Oliver Wood has to yell at Harry for being too much of a gentleman and not pushing her out of the way to get to the Snitch.
Finally, Harry spies the Snitch, but as he speeds to catch it, his attention is drawn down toward three Dementors walking alongside the field. Without thinking, Harry casts a Patronus in their direction, and he catches the Snitch easily, winning the game. Only afterwards does he discover that the Dementors were, in fact, several Slytherins, including Malfoy, dressed in cloaks with the intention of unseating Harry. They are punished severely by McGonagall, much to everyone's delight, and Harry and his friends head to the Gryffindor common room to celebrate for the rest of the day and into the night. When Harry finally returns to his dormitory to sleep, he is woken before dawn to a scream from Ron, who claims that Sirius Black had slashed open the curtain around his bed. Everybody panics, and when McGonagall asks Sir Cadogan if he let anyone into Gryffindor Tower, the knight answers yes, that the intruder had all of the passwords written on a slip of paper, which Neville Longbottom, it is soon discovered, had accidentally left in one of the corridors.
After the second Black break-in, Hogwarts tightens its security measures. Doors are taught to recognize Black's face, and the Fat Lady's portrait is returned and guarded by several trolls. Neville is not given Gryffindor's password. One afternoon Harry and Ron receive an invitation to visit Hagrid for tea, and when they do, Hagrid lectures them on shunning Hermione, who he says has been heartsick at the loss of their friendship. "I thought you two'd value yer friend more'n broomsticks or rats," he finally says.
Another Hogsmeade visit comes around, and this time Harry goes through the tunnels with his invisibility cloak. In Hogsmeade, he and Ron visit the Shrieking Shack, the most severely haunted house in Britain, and when they (or really just Ron, because Harry is invisible) are taunted by Malfoy and his cronies, Crabbe and Goyle, Harry throws mud at them from under his cloak, providing both Ron and himself great amusement until the cloak slips off and reveals his head. Harry runs back to Hogwarts, but not before Malfoy has reported to Snape what had happened. Harry hides his cloak in the tunnel just in time, because Snape greets him in the hallway soon after he has emerged and summons him into his office, where Snape insults Harry's troublemaking tendencies and compares his arrogance to that of his father. Harry is furious and yells at Snape to shut up. Snape is furious, and demands that Harry empty his pockets. He finds the map, which insults Snape rather than revealing its secrets. Snape summons Lupin through his fireplace, and Lupin arrives, looks at the map and excuses it as a trick from Zonko's joke-shop. At that moment, Ron arrives and assures them all that he had bought it for Harry months ago. Snape is forced to let the boys go, but Lupin calls them into his office and scolds them gravely for having the map in their possession when Black was on the loose, and he notes that the map-makers may be trying to lure them out of the castle. "Your parents gave their lives to keep you alive, Harry," he tells them. "A poor way to repay them—gambling their sacrifice for a bag of magic tricks." As Harry and Ron walk away, they are accosted by Hermione, who informs them that Buckbeak lost the case and is going to be executed.
Chapter Thirteen is triumphant. Harry has the Firebolt in his possession once again and he can soar through the skies. He feels somewhat apprehensive and curious about Cho Chang; this is the first time in this series that Harry is ever really shy around a girl. During the game, what appears to be a triumph over three Dementors is really just a prank played by Malfoy. Harry still feels confident enough to cast a patronus, and still wins the game. The jubilant feelings within Gryffindor house run loud and late. Only in the middle of the night is the dark shadow of Black cast upon their tower. It is peculiar that Black does not even attempt to go after Harry; this is one sign that his escape motive is not exactly what it originally seemed.
Harry is always questioning his surroundings and enemies, but in Chapter Fourteen, he is forced to reconsider his own actions. This happens first at Hagrid's house, when Hagrid scolds Ron and Harry for shunning Hermione for the broomstick and cat incidents. Later, this happens when Lupin saves Harry from a furious Snape, taking the Marauder's Map and then saying gravely to Harry that his parents' sacrifice should have made him take more precautions with his life, instead of sneaking into Hogsmeade with Black on the loose. This is one of the only instances in which Harry's character is called into question. He cares deeply about Hermione, but he is undeniably furious when she intrudes by turning his broomstick in to the professors.