"I can make bad things happen to people who annoy me. I can make them hurt if I want to."
-- Tom Riddle (HBP 13)
First, Harry and Dumbledore briefly discuss Mundungus and Draco, and Dumbledore discusses Merope Gaunt with Harry again. Together, they then view a memory of Dumbledore’s, in which he visits Tom Riddle’s childhood orphanage to invite him to Hogwarts. Dumbledore learns Riddle’s history and discovers that he has already been using magic, hates his name, likes to steal and collect trinkets, and neither has nor desires friends. (HBP13)
Timeline Notes
We know from HBP12 that this lesson falls roughly "halfway through October."
Commentary
Notes
The title of this chapter ("The Secret Riddle) is a nice play on words.
Viewing this memory of Dumbledore's in the pensieve, Harry notices that all the orphans "were all wearing the same kind of grayish tunic." These sound somewhat similar to the shabby, crude garments enslaved house-elves fashion for themselves. -BB
It is curious that Riddle immediately assumes that at least one of his parents must have been a witch or wizard in order for him to be one. Dumbledore had not told him anything about how magical ability and heredity work. Maybe this indicates that the boy already had a preoccupation with notions of birthright and ancestry, but perhaps that is not entirely unexpected, coming from an orphan; it could have been merely a grasping attempt to learn something about his parents. However, his certainty that his could not be magic since she died does suggest the intermingled natures of his fear of death and his belief in the supremacy of wizards.
Voldemort purchased his diary on Vauxhall Road in London (CS13), and the closest orphanage to that location in the 1920s was the Stockwell Orphanage, begun in the mid-1800s by the famous preacher 
Charles Spurgeon. The Stockwell Orphanage might have been the place where Tom Riddle grew up in misery, although by all accounts it was not a repressive place of the type we imagine fromOliver Twist. Also, according to the original charter, children stayed at the Stockwell Orphanage only through age 14, and Riddle probably lived at his orphanage through age 17. We now know that Riddle's orphanage had girls, too - all but eliminating this one as a possibility.