Sirius finds him covered in dust looking for more Black family relics.
Kreacher seems happier than usual, and he keeps staring at Harry with great interest.
Sirius's moods are going sour now that everyone is preparing to go back to Hogwarts.
On the last day of the holidays, Professor Snape comes to Number Twelve for a talk with Harry.
Harry finds Sirius and Professor Snape sitting at opposite ends of the kitchen table glaring at each other.
Professor Snape is there on Dumbledore's orders. Once school starts again, Professor Snape is going to be giving Harry extra lessons in Occlumency, which is the "magical defense of the mind against external penetration" (24.30).
Sirius shouts at Professor Snape, "If I hear you're using these Occlumency lessons to give Harry a hard time, you'll have me to answer to" (24.43).
Professor Snape claims that Harry is "so arrogant that criticism simply bounces off of him" (24.46).
Sirius draws his wand on Professor Snape, and Harry jumps over the table to get between them.
At this tense moment, the whole Weasley family comes bustling in.
Mr. Weasley announces, "Cured! [...] Completely cured!" (24.59).
Then they all notice that something seems to be wrong with this scene.
Sirius and Professor Snape lower their wands.
Professor Snape sweeps out after reminding Harry of his extra lessons.
The next day, they all head back to Hogwarts on the Knight Bus, escorted by Tonks and Lupin.
Before Harry leaves, Sirius gives him a package that contains "a way of letting [Sirius] know if Snape's giving [Harry] a hard time" (24.76).
On the Knight Bus, Stan Shunpike the conductor (see Book Three) starts asking questions: "You keepin' well, then, 'Arry? I seen your name in the paper loads over the summer, but it weren't ever nuffink very nice. I said to Ern, I said, 'e didn't seem like a nutter when we met 'im, just goes to show, dunnit?" (24.96).
Finally, the Knight Bus arrives at the gates of Hogwarts.
Lupin reminds Harry, "And listen [...] Harry, I know you don't like Snape, but he is a superb Occlumens and we all – Sirius included – want you to learn to protect yourself, so work hard, all right?" (24.107). Harry agrees.
Back at school, to cover up that he's taking Occlumency lessons, Harry has to tell everyone that he's doing remedial potions.
Harry asks Cho to come with him to Hogsmeade on Valentine's Day. She looks thrilled.
That night, Harry goes down to Professor Snape's office.
Professor Snape looks at Harry with visible dislike, and says, "The Headmaster has asked me to teach you Occlumency. I can only hope that you prove more adept at it than at Potions" (24.139).
The reason that Harry has to learn Occlumency is that he has "some kind of connection" (24.157) with Voldemort that Dumbledore wants Harry to block.
Harry doesn't understand why he should stop this link – after all, it's been useful, right? Thanks to the link, they were able to find Mr. Weasley in time to save his life!
Professor Snape warns Harry that now Voldemort knows Harry has seen through his mind.
The night when Harry saw through Voldemort's snake's eyes, Voldemort realized that they have this connection.
Professor Snape continues, "He has also deduced that the process is likely to work in reverse; that is to say, he has realized that he might be able to access your thoughts and feelings in return" (24.179).
Voldemort might be able to make Harry do things.
So, Harry has to learn Occlumency.
Professor Snape tells Harry to stay calm, purge himself of emotions, and do whatever he can to throw Professor Snape out of his mind.
Then, Professor Snape jumps into Harry's mind. Harry has difficulty resisting him, and it just gets worse and worse.
Harry sees Cedric Diggory lying dead on the ground, and Snape shouts, "Get up! You are not trying, you are making no effort. You are allowing me access to memories you fear, handing me weapons!" (24.210).
Professor Snape gives Harry one last try to repel him from Harry's mind.
Harry sees the long, windowless corridor he has been dreaming of.
He realizes that it is in the Department of Mysteries at the Ministry of Magic. Mr. Weasley had been there the night that he was attacked.
Professor Snape warns Harry not to think about the Department of Mysteries.
Professor Snape sends Harry off with the instruction, "You are to rid your mind of all emotion every night before sleep; empty it, make it blank and calm, you understand?" (24.239).
Harry's scar aches, and he feels shivery and strange.
He tells Hermione and Ron that the weapon Voldemort wants must be in the Ministry of Magic.
In his dormitory, Harry feels sick again. He suddenly feels intense pain in his scar: "He did not know where he was, whether he was standing or lying down, he did not even know his own name" (24.274).
Maniacal laughter rings out and he feels absolutely, totally happy.
Then, Ron slaps Harry in the face and the laughter dies away.
Harry realizes that he was the one laughing.
Something has happened, something that has made Voldemort very happy.
The Occlumency lesson seems to have weakened Harry's defenses rather than strengthening them.