Over the following weeks, Dumbledore is mysteriously absent from the school for long stretches of time. Meanwhile, Harry is becoming increasingly obsessed with the Half-Blood Prince's book, finding that it contains not only potion instructions, but some mischievous hexes which seem to have been invented by the Prince himself. Harry tries them out on his enemies, to the approval of everyone but Hermione. One morning, he tries out the Prince's spell "Levicorpus" on Ron, [[{{Irony}} thinking that the Prince has proved to be a much more effective teacher than Snape]]. Ron is (eventually) amused by the incident, but Hermione very much is not. Hermione argues that the Prince was probably on TheDarkSide, but Harry and Ron remain convinced that the Prince's spells are just innocent fun. At this point, Ginny arrives and gives Harry a piece of parchment indicating when Dumbledore's next private lesson will be.

Later in Hogsmeade, the Trio finds that Zonko's has been boarded up. In Honeydukes, they meet Slughorn, who amiably asks Harry why he has not shown up at the last three Slug Club meetings. Harry says he's had Quidditch practice and indeed he's been deliberately scheduling practices to conflict with Slughorn's meetings. Outside the Three Broomsticks, the Trio catches Mundungus Fletcher trying to sell stolen items from Grimmauld Place. He escapes by Disapparating and Tonks comes by to calm down an enraged Harry. After spending some time in the pub, the Trio heads back to Hogwarts with Katie Bell (one of the {{Living Prop}}s on the Gryffindor Quidditch team since book one) and her random friend. The two girls fight over a package and suddenly Katie flies six feet up in the air with a blank expression on her face! Then she starts screaming and falls back to the ground, writhing insanely and still screaming. Harry runs for help and finds Hagrid, who carries Katie up to the school. The Trio looks at the torn package, finding it contains an opal necklace which Harry recognizes as a cursed item he saw in Borgin and Burkes [[Recap/HarryPotterAndTheChamberOfSecretsC4AtFlourishAndBlotts years ago]]. Katie's Random Friend explains that Katie left the bathroom holding the package, saying that she had to deliver it to someone at the school. As she says this, she realizes that Katie must have been acting under the Imperius Curse.

Later in Professor [=McGonagall's=] office, Harry says that he thinks Malfoy is responsible, causing Ron and Hermione to act embarrassed. He tells [=McGonagall=] about Malfoy's visit to Borgin and Burkes, theorizing that the item he purchased was the necklace. [=McGonagall=] decides that this is insufficient evidence and reveals that Malfoy couldn't have been in Hogsmeade anyway as he's been in detention with her. As the Trio heads back to the common room, they speculate as to who the package was meant for. Harry remains convinced that Malfoy is responsible, pointing out that he could have an accomplice.