Back at Hogwarts, everyone seems to have the winter blues.
Ron is starting to get a little overwhelmed by Lavender's affections.
There's also trouble in paradise for Ginny and Dean.
Fortunately for the sixth years, Apparition lessons are on the way, proving to be a good distraction. Apparition is a means of transportation in the Wizarding world in which a wizard can travel instantly from one place to another via magic. In order to be able to Apparate legally, a wizard or witch has to be at least seventeen years old and pass a test. The sixth years will soon be able to learn how to Apparate in preparation for the test.
Ron is elated by this prospect.
Harry returns to Dumbledore's office for another private lesson.
He tells Dumbledore about his rough encounter with Scrimgeour, and Dumbledore is moved by Harry's loyalty to him and by Harry's unwillingness to divulge any of Dumbledore's information to the Minister.
Harry and Dumbledore travel into the Pensieve to see two memories.
The first memory Dumbledore secured from Morfin Gaunt before he died in Azkaban Prison. In it we see Voldemort seeking out the Gaunt family home and encountering his uncle, Morfin, there.
Morfin is as mean and wild as ever, and mistakes Voldemort for Tom Riddle, Sr. until Voldemort starts speaking to him in Parseltongue.
Morfin tells Voldemort about the Gaunt family history, pointing out the prized Gaunt ring on his finger. He also tells Voldemort where Tom Riddle, Sr. lives.
But then the scene goes black. The memory ends.
According to Dumbledore, the next thing Morfin knew, he was lying on the floor of the house, his ring gone.
Morfin, a known Muggle hater, was charged with the murder of Tom Riddle, Sr. and his parents.
Dumbledore can only guess what went on, but he believes that, after visiting Morfin, Voldemort went to the manor house where he found his father and his father's parents. He killed all three Muggles.
Dumbledore believes that Voldemort cast a spell on Morfin, causing him to forget Voldemort's actions, and believe that he himself had killed the Riddles. Morfin even confessed to murdering the Riddle family.
Lastly, Dumbledore knows that Voldemort stole the Gaunt family ring.
Next, Dumbledore and Harry travel into the Pensieve to examine a memory of young Tom Riddle during his time at Hogwarts.
In it we see a group of boys gathered at Slughorn's for a casual party. Tom is clearly the leader of the group, and he's also wearing the Gaunt family ring, which means he's already killed the Riddles.
Tom Riddle asks Slughorn what a Horcrux is, and, before we can hear the reply, a fog fills the memory.
It would seem that Slughorn has put up a wall preventing anyone from seeing what comes next. Slughorn has refused to give Dumbledore the full, original memory.
Dumbledore gives Harry a very serious and very important homework assignment: to retrieve the full memory from Slughorn at all costs.