We pick up right where the last chapter left off: The entire student body staring at the motionless form of Mrs Norris, with an ominous message written in blood on the wall. Filch and the teachers soon show up, and the caretaker immediately accuses Harry of murdering his cat. Dumbledore takes Harry, Ron and Hermione to Lockhart's office, accompanied by Filch, [=McGonagall=], Snape and Lockhhart.

Dumbledore deduces that Mrs Norris is not dead, but is just petrified. Filch again blames Harry for doing the deed, claiming that Harry knows that he's a "Squib", whatever that is. After Harry protests, Snape suggests that Harry and his friends might have been in the wrong place at the wrong time, but then asks why they weren't at the halloween feast. When the trio explain about the Deathday Party, Snape then asks why they went up to that corridor in the first place. Harry makes up an excuse, deciding not to mention the hissing voice he heard coming from the walls.

Snape senses that Harry's hiding something, and tries to use this as an excuse to take him off the Gryffindor Quidditch team, but [=McGonagall=] and Dumbledore refuse to punish Harry before he's been proven guilty of anything. Dumbledore assures Filch that they will be able to revive Mrs Norris with a potion made from Professor Sprout's mandrakes, and dismisses everyone. Talking with his friends, Harry's decision to not tell the teachers about the mysterious voice is justified by Hermione, who warns him that "even in the wizarding world, hearing voices isn't a good sign". We also learn that a squib is a person with two magical parents [[{{Muggle}} who has no magical powers of their own]]. It certainly explains why Filch had the Kwikspell letter, and why he hates all the students so much; he's bitter about them having magic.

The next day, the trio return to the crime scene. Mrs Norris is gone, as is the water puddle, but the bloody letters are still there, and there's an interesting new addition to the scene; a line of spiders travelling across the castle. We also get an interesting little tidbit about Ron; he's been scared of spiders ever since an incident from years ago when Fred transfigured Ron's teddy bear into a giant spider after Ron broke his toy broomstick. The trio investigate Myrtle's bathroom, but fail to learn anything, and are chased off the scene by Percy shortly afterwards.

After learning that all the library's copies of ''Hogwarts: A History'' have been borrowed, Hermione asks Professor Binns about the Chamber of Secrets during History of Magic. While initially reluctant to play MrExposition, since his subject is about facts and not myths and legends, Binns agrees to tell the class what they want to know, and starts by talking about the school's early history. In the past, one of Hogwarts's co-founders, a great wizard going by the name of Salazar Slytherin, had a falling out with the the other three founders: Godric Gryffindor, Helga Hufflepuff, and Rowena Ravenclaw. And before anyone asks, yes, the Hogwarts Houses [[CaptainObvious are named after those founders]]. Slytherin disapproved of taking on non-pure blood students, muggleborn ones in particular, and left the school when he was unable to convince the others to take his side.

According to legend, Slytherin built a hidden chamber in the school, and put in it a monster that only his descendents would be able to control, with the intention that one of said descendents - The Heir of Slytherin - would one day open the chamber, unleash the monster, and purge the school of its muggleborn students. His exposition done, Binns insists that the Chamber of Secrets isn't real; the school has been searched many times, and if wizards and witches of Dumbledore's calibur can't find it, how can it exist?

Harry, Ron and Hermione remain convinced that there's truth to the legend, and start talking about who the Heir of Slytherin might be. Ron immediately suggests Malfoy; he hates Muggleborns and was all "you'll be next, mudbloods" last night, and when Hermione expresses disbelief, Harry points out that the Malfoys have been sorted into Slytherin house for centuries; they could very well be Slytherin's descendants. Hermione states that if Malfoy really is Slytherin's Heir, he's not going to admit it, and neither will Crabbe and Goyle, but there might be another way to get the truth out of him: Polyjuice Potion - a potion that allows one to transfrom into an exact duplicate of another. Hermione proposes that the Trio make this potion, use it to impersonate Crabbe and Goyle, and question Malfoy.

And right from the start, they encounter a setback; the book containing the Polyjuice recipe - ''Moste Potente Potions'' - is in the restricted section of the library, requiring permission from a teacher to access. Hermione suggests that they claim to be interested in the theory, and Ron starts to say that someone would have to be really thick to buy that story...

Spoiler for the next chapter: [[spoiler:They ask Lockhart]].