Couples are falling apart everywhere: Ginny and Dean are locked in a heated argument, and Lavender and Ron (much to Hermione's delight) are also on shaky ground.
Harry is summoned to his next lesson in Dumbledore's office where he finds Professor Trelawney. She's angry that she's not the only Divination professor, and she threatens to quit.
When Trelawney leaves, Dumbledore asks Harry if he has procured the Horcrux memory yet.
Harry has not and tells Dumbledore, and lamely says that he's been busy with other things.
Dumbledore grows stern and serious, reiterating to Harry just how important and vital that particular memory is. He implores Harry again to do everything in his power to retrieve the memory from Slughorn.
Dumbledore and Harry use the Pensieve to travel into two memories.
The first memory is of a young Voldemort who works at Borgin and Burkes.
At this time, Voldemort's job is to travel from house to house, convincing witches and wizards to sell their prized possessions and family heirlooms to Borgin and Burkes.
Here, we find him visiting Hepzibah Smith, a wealthy, elderly witch.
Hepzibah, who's clearly enamored of the handsome, young Voldemort, shows him her two most prized treasures: the golden Hufflepuff cup and the golden Slytherin locket.
Both items are ancient and are extraordinarily precious. Voldemort's eyes flash red at the sight of them, and it's obvious that he wants them desperately.
The memory ends.
Dumbledore tells us that two days later, Hepzibah was found dead, her treasures stolen, and her house elf, Hokey, blamed.
This is apparently the first time that Voldemort kills for gain instead of out of revenge.
Next, we travel into Dumbledore's memory of encountering Voldemort at Hogwarts some ten years after the Dark Lord had himself graduated from the school.
In this memory we see Voldemort ask Dumbledore for a teaching position at Hogwarts, a request Voldemort made once before when he had just graduated.
Through a series of questions, Dumbledore is able to discern that Voldemort doesn't really want to teach young wizards and witches – he wants to influence them and to be near the powerful knowledge that Hogwarts holds.
Dumbledore implies that he knows about the evil deeds Voldemort has carried out over the last ten years, and he tells Voldemort that it is clear he still hasn't learned the power of love.
Voldemort tells Dumbledore he hasn't found any evidence in the world suggesting that love is powerful or important. Voldemort tells Dumbledore that he has pushed the boundaries of magic in a way no wizard has ever done before.
This freaks Dumbledore out a little bit, but he doesn't lose his cool. He expresses regret at having been unable to help Voldemort start a new leaf and find love in the world.
As a result of Dumbledore's refusal to give Voldemort that Defense Against the Dark Arts teaching job that Voldemort so wanted, Hogwarts has never since been able to keep a D.A.D.A. professor for longer than one year.