Chapter 23 - "Horcruxes" - In which Harry learns that Dumbledore has returned, races off to his office, and with him watches Slughorn's memory, where Riddle learns what Horcruxes are and contemplates making more than one. Dumbledore explains his suspicions that Riddle made six, including the now-destroyed ring and diary, the locket, the cup, and Nagini. Dumbledore promises Harry can join him in destroying the next one, and explains to Harry what love - and the prophecy - really mean.
One More Try for a Memory
At dinner, [Harry] learns that [Hermione] has passed her [Apparition] test but [Ron] has not, and they collectively decide that [Harry] needs to take his [Felix Felicis] tonight to get [Slughorn]'s memory.
Harry Uses Felix Felicis to Great Effect
[Harry] takes a swig of [Felix Felicis] and with full confidence decides to head down to [Hagrid]'s [hut], alarming [Ron] and [Hermione]. As he leaves [Gryffindor Tower], he hears [Lavender] accosting [Ron] and [Ginny] chewing out [Dean Thomas], putting him in an even better mood.
After sneaking out the front door, [Harry] runs into [Professor Sprout] and [Professor Slughorn] in the [vegetable patch], and invites [Slughorn] to go with him to [Hagrid's hut] to help bury [Aragog].
[Harry] and [Hagrid] prepare to bury [Aragog], and are soon joined by [Professor Slughorn]. [Slughorn] sneaks some of [Aragog]'s venom and delivers a brief eulogy, and the three head back into the [hut].
Drinking wine together in [Hagrid's hut], [Harry], [Hagrid], and [Slughorn] sing songs and talk about [Harry]'s parents - and [Harry] convinces [Slughorn] to give up his memory of [Riddle] and [Horcruxes].
[Harry] walks back into the castle with the newly obtained memory and heads to [Gryffindor Tower], but the [Fat Lady] pretends the [password] has changed and won't let him in. When [Nearly Headless Nick] informs [Harry] that [Dumbledore] has returned, though, he heads off to [Dumbledore's office] instead.
The Real Memory
[Harry] runs up to [Dumbledore's office] excitedly and together the two of them watch the memory [Harry] got from [Slughorn].
At the end of a [Slug Club] meeting, [Tom Riddle] asks [Professor Slughorn] for information on [Horcruxes], and particularly wizards who might split their souls into seven parts.
After watching [Slughorn]'s full memory, [Dumbledore] explains his theory on [Voldemort]'s [Horcruxes] to [Harry] and together they discuss the fight to destroy them, the power of [Harry]'s love, and the meaning and power of the [prophecy].