"I suppose the real reason Ginny Weasley's like this is because she opened her heart and spilled all her secrets to an invisible stranger."
-- Tom Riddle
Harry finds an unconscious Ginny, meets Tom Riddle (who has had Ginny in his power through the diary), and hears his story. Fawkes the phoenix arrives with the Sorting Hat. Riddle (Voldemort) calls the basilisk to kill Harry, but Fawkes intervenes and together they kill the basilisk, and by driving a serpent fang through the diary, get rid of Riddle as well.
Calendar and Dates
The action of this chapter takes place on the same day as that of the previous chapter.
Interesting facts and notes
All of the events in this chapter take place within the Chamber of Secrets.
It was ancient and monkeyish, with a long, thin beard that fell almost to the bottom of the wizard's sweeping stone robes
yet here he stood, a weird, misty light shining about him, not a day older than sixteen.
Harry's guess as to diary-Riddle's age is borne out by Riddle's own words a little later on.
twirling Harry's wand between his long fingers
No mention of a ring on Riddle's wand hand, and at this point it seems unlikely that Harry would've missed it if it had been present, since Harry is taking special notice of Riddle's fingers. Considering the significance of the ring to Riddle after he had acquired it, and his habit of wearing it during his later years at Hogwarts (HBP23), it seems odd that diary-Riddle isn't wearing it. We know that Riddle acquired the ring before implementing his plan of creating multiple Horcruxes (HBP23), so it seems likely that he would have created the diary Horcrux after his acquisition of his grandfather's ring.
Powerful enough to start feeding Miss Weasley a few of my secrets, to start pouring a little of my soul back into her...
This remark takes on somewhat more depth than is at first apparent, once Harry learns about Horcruxes nearly four years later.
It had taken me five whole years to find out everything I could about the Chamber of Secrets and discover the secret entrance...
From Dumbledore's memory of his first meeting with Tom Riddle (HBP13), we know that Riddle never knew about Hogwarts prior to entering as a first-year student, so he could not have begun searching for the Chamber before his first year at Hogwarts. Riddle's memory of framing Hagrid (CS13) and his remarks in this chapter indicate that he had found the Chamber by the time he was sixteen. Since his birthday falls at the New Year, he turned sixteen halfway through his fifth year. Altogether, these pieces of information suggest that Riddle began searching for the Chamber during his first year at Hogwarts, and found it either very near the end of his fifth year or at the beginning of his sixth year.
I decided to leave behind a diary, preserving my sixteen-year-old self in its pages...
Riddle is speaking nearly the literal truth here. He didn't just preserve a memory of himself, but a part of his soul by creating a Horcrux. If Riddle's sixteen-year-old self is an indication of when the Horcrux was created (i.e., if it was created when he was about that age), perhaps either the basilisk's killing of Myrtle (if a killing by such indirect means would work) or the more direct murders of his father and paternal grandparents (GF1) were used to create the Horcrux.
he waited for Riddle to stop laughing with his courage mounting.
Phoenix song has this effect (FB).
He, Harry, had Fawkes and the Sorting Hat, neither of which would be much good in a duel.
Harry is about to eat these words regarding both Fawkes and the Sorting Hat, of course. Furthermore, three years from now Fawkes will save Dumbledore from Voldemort's Killing Curse during their duel in the Atrium at the Ministry of Magic (OP36).
"Probably the only two Parselmouths to come to Hogwarts since the great Slytherin himself."
Judging by Riddle's mother's immediate family, all three of whom appear to have been Parselmouths and to have had magical training (HBP10), this doesn't seem likely. Riddle had had brief contact with his maternal uncle at the time of his murder of his own father's family, so he should have realized the likelihood of other Parselmouths having attended Hogwarts since Slytherin's departure (HBP17).
However, all that nit-picking detail wouldn't make anywhere near as dramatic a speech, and Riddle doesn't seem like the type to sacrifice style for accuracy, does he?
Exceptional character moments
Riddle seems prone to overlook details about certain kinds of magic, in this case the properties of phoenix tears.
"Odd sort of place this, isn't it?"
"Amazing! Amazing! This is just like magic!"