Harry and Ron discuss the recent events, and particularly their effect on Percy. They then decide to go talk to Hagrid, with the help of Harry's Invisibility Cloak.

Startling Revelations in Hagrid's Hut
With some difficulty Harry and Ron manage to sneak out of the castle and get to Hagrid's hut. There, Hagrid is extremely nervous, greeting them with a crossbow, and says little. Before the boys can ask any questions, though, there is a knock on the door.
With Harry and Ron hiding under the Invisibility Cloak, [Dumbledore] arrives with Cornelius Fudge to tell Hagrid he is being taken to [Azkaban] - and their arrival is soon followed by that of Lucius Malfoy, announcing that [Dumbledore] is also being removed from Hogwarts. As they leave, [Dumbledore] announces that he has not truly left Hogwarts, and Hagrid lets Ron and Harry know they need to follow the spiders.
Chapter 15 - "Aragog" - In which tension mounts in Hogwarts as everyone fears another attack - except Draco Malfoy, who is enjoying the situation. Acting on Hagrid's hint about following spiders, Harry and Ron go into the Forbidden Forest, find the Ford Anglia, are captured by acromantulas, learn more about the Chamber of Secrets, and are rescued by the car.
As summer approaches, security is intense around Hogwarts and things feel wrong to Harry without Hagrid outside the windows. Harry, meanwhile, keeps thinking about the final words he heard from Hagrid and [Dumbledore].
Schoolwork
In Potions class, Malfoy brags about his father's removing [Dumbledore] from Hogwarts and asks Snape to apply for the [Headmaster] position. Malfoy continues gloating throughout class, and makes disparaging comments about [Mudbloods].
In Herbology class, [Ernie Macmillan] apologizes to Harry, who accepts but stamps it out quickly when [Ernie] suggests Malfoy might be behind the attacks. Then, Harry notices spiders scurrying toward the Forbidden Forest - and he and Ron decide to take Fang and follow.
In Defence Against the Dark Arts, Lockhart brags he knew all along that Hagrid was behind the attacks, and Harry and Ron, in their anger, decide to follow the spiders that night.
A Conversation With Aragog
After the Gryffindor common room empties out, Harry and Ron duck under the Invisibility Cloak, fetch Fang from Hagrid's hut, and go after the spiders, deep into the Forbidden Forest.
Deep in the Forbidden Forest, Harry and Ron start as they hear something moving - but soon relax when they discover it's the Ford Anglia. They realize they've lost sight of the trail of spiders, but Ron is soon distracted by something bigger.