Chapter 13 - "The Very Secret Diary" - In which Myrtle's toilet floods, Harry finds Tom Riddle's diary which he shows to a now fur-free Hermione, and they begin a search to discover who the owner was. Lockhart stages a Valentine's party complete with dwarfs as cupids. That night Harry learns the secret of the diary, goes back in time, and discovers - or so he believes - that it was Hagrid who last opened the Chamber of Secrets.
The Polyjuice Potion Adventure
Back in the bathroom, [Harry] and [Ron] discover that [Hermione] accidentally transformed into a [cat]. Despite [Moaning Myrtle]'s goading, however, they convince her to go to the [hospital wing].
As the weeks pass, [Hermione] stays in the [hospital wing] with frequent visits from [Harry] and [Ron]. There they discuss their inability to learn more about the [heir of Slytherin], and [Ron] discovers a card from [Lockhart] under [Hermione]'s pillow.
Harry Finds the Diary
[Harry] and [Ron] are leaving the [hospital wing] when they hear [Filch] screaming a floor above. They run up to discover a crying [Moaning Myrtle], upset because a [diary] has been thrown at her. [Harry] picks up the diary despite warnings from [Ron], discovers it belongs to [T.M. Riddle], and pockets it.
[Hermione] gets out of the [hospital wing] and chats with [Harry] and [Ron] about [Riddle's diary]. They realize that [Riddle] was at school around the time of the [Chamber of Secrets]' first opening, but can't get it to do anything.
Though unable to explain why, [Harry] hangs on to [Riddle's diary]. The trio tries to find out more about [Riddle], but can't come up with much.
As time passes the students of [Hogwarts] gradually become more hopeful. [Madam Pomfrey] is happy that the [Mandrakes] are maturing, and [Lockhart] thinks he's responsible for stopping the attacks. [Peeves], though, is still singing of [Harry]'s guilt, and [Ernie Macmillan] remains suspicious as well.
Valentine's Day and a Conversation With Tom Riddle
[Harry] walks into the [Great Hall] and is shocked to find it decorated - by [Lockhart], of course - for Valentine's Day. [Lockhart] announes a variety of festivities for the day, much to the consternation of the other teachers.
As Valentine's Day progresses, [dwarfs] periodically interrupt classs to deliver valentines - but none so memorable as a singing telegram for [Harry]. In the chaos surrounding it, [Harry]'s bag splits and [Malfoy] grabs [Riddle's diary] - which, [Harry] soon notices, was untouched by the ink that spilled over the rest of his books.
[Harry] goes to bed early in order to try writing in [Riddle's diary] - and soon discovers that [Riddle], in the [diary], writes back. [Riddle] tells [Harry] he knows about the [Chamber of Secrets], and offers to show [Harry] what happened.