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
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.
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.