Harry Potter and the Half-Blood Prince

At their next lesson, Dumbledore asks Harry if he was able to retrieve the memory from Slughorn. Harry has not done so but promises to try harder. Dumbledore is extremely disappointed. They return to studying Voldemort. Dumbledore explains how Voldemort had been an excellent student. Many faculty members suggested that he apply for a position at the Ministry after graduation. Instead, Voldemort asked if he might remain at Hogwarts as an instructor of Defense against the Dark Arts. Then-Headmaster Dippet told Voldemort that he was too young but should consider reapplying later. Voldemort took a job working at Borgin and Burkes, persuading people to part with Dark or unusual objects. Harry and Dumbledore enter the Pensieve to view a memory of Hokey, a House Elf to a very rich old witch named Hepzibah Smith.

Hepzibah is enthralled by Voldemort and offers to show him two extremely rare objects, a small golden cup and a locket. Hephzibah tells Voldemort that the cup belonged to Helga Hufflepuff, one of the four founders of Hogwarts. The gold locket bears Slytherin's mark and is the same locket that Merope sold to Borgin and Burkes many years earlier. Voldemort's eyes turn scarlet as Hepzibah explains how she bought the locket from the shop and refuses to give it up. Harry and Dumbledore return to Hogwarts. Dumbledore explains that Hepzibah Smith died days after the visit they witnessed, supposedly poisoned by Hokey, who later confessed to the crime. Harry and Dumbledore agree that Voldemort must have murdered Hepzibah and changed Hokey's memory so that she would confess to the crime. After Hokey was convicted, Hepzibah's family realized that the locket and the cup were missing. Around the same time, Voldemort left his job at Borgin and Burkes and was not seen or heard from for a very long time. Dumbledore notes that Voldemort has now committed another murder, this time killing for gain rather than revenge.

The next memory they witness is one of Dumbledore's, from ten years after Hepzibah's death. Dumbledore is seated in his office at Hogwarts when Voldemort knocks and enters. Voldemort reminds Dumbledore that he no longer goes by the name Tom Riddle. Voldemort again expresses his interest in teaching Defense Against the Dark Arts, but Dumbledore is skeptical and denies him. Harry and Dumbledore return to Dumbledore's present-day office. Dumbledore reminds Harry that ever since he denied Voldemort the position of Defense Against the Dark Arts professor, Hogwarts has not been able to keep a Defense teacher longer than one year. Later, Harry finds a new spell, Sectumsempra, scrawled in the margins of his Potions textbook, with the words “For Enemies.” Kreacher and Dobby reappear to report back. Dobby tells Harry that while Draco is not breaking any rules, he makes regular trips to the seventh floor, bringing other students with him to stand guard. Harry remembers the Room of Requirement on the seventh floor, which transforms into whatever its transformer requires.

Harry decides to sneak up on Draco when he is in the Room of Requirement, but Hermione reminds him that unless he knows exactly what Draco is doing, he cannot summon the Room, because he won't know what he needs it to be. Kreacher and Dobby leave. Harry thinks Draco must have stolen some Polyjuice Potion from Slughorn and has been using it on Crabbe and Doyle, transforming them into first-year girls to avoid suspicion.

The next weekend, Ron and Hermione go to Hogsmeade to practice Apparition. After they leave, Harry attempts to get into the Room of Requirement to see what Draco is doing. After thirty minutes of trying, Harry still cannot gain access to the room. Frustrated, Harry rushes at the wall. His Invisibility Cloak slips off, and Tonks suddenly appears, looking thin and haggard. Tonks asks Harry if he's heard from any members of the Order, but Harry explains that since Sirius's death, no one writes to him anymore. Tonks's eyes fill with tears. Later, Harry tells his friends about running into Tonks and that he suspects she may have been in love with Sirius.

Dumbledore believes that Voldemort was interested in teaching at Hogwarts because of the proximity the position would offer to strong magic and young, impressionable wizards. But Dumbledore also thinks that, as an orphan, Voldemort considered Hogwarts his only real home. Harry has always felt similarly, having long despised living with his horrible aunt, uncle, and cousin, where magic was not allowed to be discussed or alluded to. When Harry came to Hogwarts five years ago, it was the first time he ever felt like he had a real home, with a real family. Once again, Harry observes a similarity between his own trajectory and Voldemort's history. Rowling is careful to emphasize that although Harry and Voldemort came from extremely similar origins, and were forced to deal with equally terrible childhoods, Harry has never been tempted to give in to the Dark Arts. Again, Harry's remarkable heart seems to be what prevents him from sharing Voldemort's tragic fate.

Harry learns that Voldemort has killed again, this time for gain and not simply for revenge, and has framed another innocent bystander for the crime. This time, Voldemort wanted to acquire Hepzibah Smith's locket and cup—although the locket was, on some level, rightfully his, Voldemort's burning desire to own Hufflepuff's cup is less clear to Harry. Obviously, the cup is a symbol of Hogwarts, which means a great deal to Voldemort. The cup is also reminiscent of the objects he pilfered from his peers at the orphanage, which he kept as proud souvenirs of his devious activities, giving them back only after Dumbledore ordered him to. Slowly, Dumbledore's insistence that Harry pay attention to repetitions in Voldemort's past is starting to make sense. Patterns are emerging, as specific behaviors are repeated again and again.

Even though Dumbledore specifically asked Harry to concentrate on retrieving an unmodified memory from Slughorn, Harry let his responsibilities slip, choosing instead to spend his time chasing Draco Malfoy around. Harry's growing obsession with Draco's whereabouts is beginning to bother his friends and distract him from his priorities. Even though Hermione reminds Harry that there is no way he will be able to gain access to the Room of Requirement without first knowing what Draco is using the room for, Harry spends an entire day trying his best to get inside and completely ignoring Dumbledore's request about Slughorn. After many failures, Harry even goes so far as to throw himself up against the wall, in a gesture of frustration more than anything else. Harry's behavior with regard to Draco is becoming increasingly bizarre and, at times, detrimental to his larger mission.

Yet again, Tonks appears to check up on Harry when his Invisibility Cloak slips off and he rams himself into the wall, trying desperately to force his way into the Room of Requirement. By now, we can be fairly certain that Tonks is not consistently rescuing Harry by coincidence, but because she has been assigned to watch over him by Dumbledore. When Harry tells Tonks that no one from the Order writes to him anymore, Tonks gets teary eyed, and Harry assumes it is because he has reminded her of Sirius's death. Lupin no longer writes to Harry because he is underground, living among the werewolves, and without Lupin and Sirius to send him letters, Harry is essentially cut off from the Order. Harry is suspicious of Tonks's tears, and begins to wonder if her intense mourning of Sirius is not indicative of a greater emotional response. Harry knows that Tonks and Sirius were never particularly close when Sirius was alive, and the only conclusion he can draw is that Tonks was always secretly in love with Sirius. Harry cannot think of another reason why the thought of Harry receiving no letters from Sirius or Lupin would make her cry.