Harry Potter and the Half-Blood Prince
Chapter 13 - The Secret Riddle
Katie Bell has been sent to St. Mungo′s Hospital. Harry has another lesson with Dumbledore and the headmaster tells him that Snape was able to help Katie Bell a little, because he knows a lot about those things. Harry tells him about his suspicion against Malfoy, and Dumbledore promises to check it. After their conversation they experience two more memories in Dumbledore′s Pensieve. The first one is about Caractus Burke, who bought a locket from a woman for only ten Galleons. The locket once belonged to Salazar Slytherin.
The second memory is about Dumbledore visiting Tom Riddle in the orphanage. This is where Dumbledore told him that he, Tom Riddle, was a wizard and that he would go to Hogwarts. At that time Tom Riddle was already very powerful for his age and he liked to collect trophies of his "victims".