Ron and Lavender have broken up, as have Ginny and Dean. Harry is ecstatic. Katie Bell recovers and returns to school. Tensions run high for the Gryffindor vs. Ravenclaw game. A few days before the match, Harry checks the Marauder’s Map and sees Draco in the boys’ bathroom with Moaning Myrtle. Harry rushes to the bathroom where Draco is crying at the sink, sobbing that unless he does something soon, he will be killed. Draco spots Harry and pulls out his wand. Harry yells “Sectumsempra,” the hex scribbled in the margins of the Half-Blood Prince’s book. Blood spurts from Draco’s face and chest, and Myrtle beings screaming. Snape bursts into the room and heals Draco’s wounds almost immediately. Snape hurries Draco to the hospital wing, commanding Harry to wait behind. When Snape returns, he asks Harry where he learned the spell, and demands that Harry bring him his Potions textbook. Harry leaves and runs into Ron, who lends Harry his Potions textbook. Harry sprints to the seventh floor and opens the Room of Requirement. Harry sees the broken Vanishing Cabinet Montague used last year. Harry hides the Half-Blood Prince’s book and runs back to the bathroom.
Snape is skeptical of Ron’s book and gives Harry detention every Saturday until the end of the term, which means Harry will have to miss Saturday’s Quidditch match. Harry’s teammates are devastated. That Saturday, when Harry is finally dismissed from detention, the Quidditch match is already over. Harry returns to the Gryffindor common room and is greeted with a huge celebration. Gryffindor won the match and the championship. Ginny runs toward Harry and throws her arms around him. Without thinking about it, Harry kisses her. Students immediately begin gossiping about Harry and Ginny. Ron chides the new couple but lets them know he has no objection. At lunch, Hermione shows Harry a newspaper article about Eileen Prince, and suggests that she may be the Half-Blood Prince. Harry receives a scroll asking him to report to Dumbledore’s office as quickly as possible.
On his way, Harry runs into a distressed Professor Trelawney. Harry asks her what happened, and she tells him that she was trying to get into the Room of Requirement to hide her sherry bottles, but when she went in, someone was there, whooping with excitement. She was hurled out of the room almost immediately. Harry tells Trelawney that she should tell Dumbledore what happened, and they head off together. Professor Trelawney tells Harry about her first interview with Dumbledore before she was hired. She was staying at the Hog’s Head, and Dumbledore came to see her in her room. Harry knows that this was when she made the prophecy about Harry and Voldemort, but Trelawney only remembers feeling funny. She and Dumbledore were interrupted by Snape, who was caught eavesdropping by a barman. Harry realizes that it was Snape who told Voldemort about Trelawney’s prophecy, thus sending Voldemort after Harry and his mother and father. Harry leaves Trelawney in the hallway and races toward Dumbledore’s office. Before Harry can confront Dumbledore, Dumbledore tells him that he has found a Horcrux and that Harry will be accompanying him to destroy it. Dumbledore tells him that the Horcrux is hidden in a cave on the coast, the same cave in which Voldemort once terrorized two children from his orphanage.
Harry tells Dumbledore that he knows that it was Snape who carried word of the prophecy. Dumbledore defends Snape, saying that he was still under Voldemort’s control and had no way of knowing that Voldemort would kill Harry’s parents. Harry is still outraged and implores Dumbledore to tell him why he trusts Snape. Dumbledore simply does. Harry tells Dumbledore about Draco’s whooping in the Room of Requirement. Dumbledore is once again unconcerned, assuring Harry that Hogwarts will be protected in their absence. Before they leave for the Horcrux, Dumbledore tells Harry that he must follow all orders Dumbledore gives him. Harry leaves to fetch his Invisibility Cloak and finds Ron and Hermione in the common room. He gives them the Marauder’s Map and the bottle of Felix Felicis and tells them to watch Snape and Draco Malfoy and to use special Galleons to contact any members of the D.A. (Dumbledore’s Army, the secret study group formed by Harry and his friends in the previous book to study Defense Against the Dark Arts) who may be able to help. Harry and Dumbledore walk to Hogsmeade together and Apparate to the shore.
Harry and Ginny’s kiss seems to happen totally naturally, without nervous prodding from either end. Even though Harry spends a great deal of time worrying about how his best friend will react to Harry kissing his sister, it turns out that Ron is actually just happy to see Harry content and relaxed and prefers his best friend to the other boys Ginny has dated. Ron jokes about giving Ginny and Harry his permission, but he is clearly not bothered by their sudden, unannounced coupling. The school gossips relentlessly about Ginny and Harry’s relationship, but Harry is simply glad that he’s getting attention for a perfectly normal event rather than for facing off with Voldemort. Rowling often contrasts the two major facets of Harry’s young life. On one hand, he is an average schoolboy, kissing girls and trying to pass his examinations, playing Quidditch and getting detention, just like every other student. Other times, however, Harry is preparing to chase down Horcruxes and arguing with the headmaster about the relative worth of another professor.
Although Harry has had considerable luck with the Half-Blood Prince’s Potions textbook in the past, the Sectumsempra spell proves to be a bit more than he can handle. Despite his intense dislike of Draco, Harry did not intend to attack Draco as violently as he did, and his own shock and fear at his act is indicative of Harry’s good heart. The fact that Draco was sobbing at the sink is also a surprising twist, as it portrays Draco as oddly sympathetic. Clearly, the stress of his predicament is taking its toll, and whatever Draco is up to, he is doing it under the threat of his own death. Rowling once again manages to make an unsympathetic character vaguely sympathetic. Just as we feel sorry for Voldemort that he had to endure such a painful childhood, we suddenly see that Draco Malfoy is actually under enormous pressure and is in a good deal of emotional pain. For Rowling, characters are rarely black and white. Draco is not a pleasant young man, but he is not emotionless, either.
Despite Harry’s ever-growing distrust of Snape, which is only accentuated by his discovery that it was Snape who leaked the prophecy to Voldemort, Dumbledore still continues to believe that Snape is loyal to the Order. Harry simply cannot understand how Dumbledore can completely ignore all the evidence that points to Snape’s inherent evilness. It hurts Harry to think that Dumbledore is being taken advantage of by Snape, and he begins to wonder if Dumbledore is growing too old and too out of touch to truly protect Hogwarts and help Harry stop Voldemort. Harry’s skepticism is natural, but Dumbledore has certainly earned Harry’s trust, and Harry can do nothing but accept that Dumbledore has good reason to believe that Snape is not betraying the Order. All of this does little to calm Harry’s nerves, however. Like his father and godfather, Harry believes that Snape is entirely untrustworthy. Once again, Dumbledore promises Harry that Hogwarts will be protected in their absence and seems strangely unconcerned that Draco was caught whooping with excitement in the Room of Requirement. Clearly, Dumbledore knows more about what goes on at his school than he lets on.
Throughout the series, Rowling has never given us reason to think that Dumbledore is anything other than a wise and powerful wizard. Accordingly, it seems highly unlikely that Dumbledore would be so incredibly nonchalant about Snape and Draco were he not in some way already clued in to their plans. Harry is bewildered by Dumbledore’s behavior, but since we can infer that Dumbledore knows things he is not telling Harry, we get a sense of foreshadowing that events will turn out in a way that will surprise Harry. Before Dumbledore and Harry leave for the cave, Dumbledore insists that Harry give his word that he will follow any and all of Dumbledore’s orders. Again, Rowling is foreshadowing events to come. Harry reluctantly promises to do whatever Dumbledore tells him to, no matter how unpleasant or disappointing, and we begin to suspect that their journey may be more tumultuous than expected—and that Dumbledore, once again, knows exactly what lies ahead.