Harry Potter and the Order of the Phoenix (novel)/Recap/C24 Occlumency
Kreacher is found lurking in the attic. Sirius is satisfied thinking that he was just trying to find some Black family relics, but Harry can't help but noticing that Kreacher suddenly seems a lot happier. He doesn't mention this as Sirius is already very depressed about the kids' imminent departure for Hogwarts. Harry wishes he could stay with Sirius since Hogwarts sucks now.
One day, Snape stops by to meet with Harry and Sirius. Dumbledore has ordered Snape to teach Occlumency to Harry this term. Ah, Occlumency -- that magical discipline which launched a thousand Slash Fics. As we will see, the subject primarily consists of Ho Yay, but there's also some actual teaching involved too. "What could this Occlumency possibly be like?" you ask. Well, Snape defines it here as "magical Defense of the mind against external penetration." And off we go.
Inevitably, an argument arises between Snape and Sirius. Basically, Snape acts as though Sirius is a layabout who actually likes being stuck in his family home and Sirius accuses Snape of still being evil. Suddenly, the Weasleys enter the room. Mr. Weasley cheerfully announces that he's been cured, but then everyone notices the scene. Snape and Sirius are pointing their wands at each other. Harry is standing between them, trying to break it up. Having been brought back to their senses, Snape and Sirius lower their wands and Snape departs.
The next day marks the return to Hogwarts. Harry is worried that Snape's comments will drive Sirius into doing something reckless in order to prove he's not a coward. Sirius gives Harry a parting gift, which he says will allow Harry to tell him if Snape is giving him a hard time. Harry privately decides never to use it for fear it could provoke Sirius into doing exactly the sort of reckless thing he's afraid he'll do. Tonks and Lupin take Harry and company back to Hogwarts on the Knight Bus. It turns out the bus contains unfastened chairs rather than beds during the daytime. After a few stops, the bus lets them off at the Hogwarts gate. Before he and Tonks leave, Lupin tells Harry that Occlumency is very important and he should try to work with Snape even if he's a jerk. Later that day, Cho points out that the next Hogsmeade weekend is on Valentine's Day and tries to get Harry to ask her out in the most obvious way possible. Being a teenage boy, Harry fails to get it, of course, but eventually he figures it out and she agrees to a date.
That evening, Harry arrives in Snape's office for his first Occlumency session. Snape sets the tone by insisting that he will be addressed as "sir". Legilimency, Snape explains, is a form of Telepathy used by Voldemort. Harry calls it "mind-reading", prompting Snape to go all Insistent Terminology and declare that the mind is not a book to be read. Legilimency normally requires eye contact, but this does not apply to Harry. The curse which failed to kill Harry created a strange connection between his mind and Voldemort's. This is why Harry sees inside Voldemort's mind from time to time. It is believed that Voldemort has recently found out about this connection and deduced that the process may be reversible, i.e. Voldemort could see inside Harry's mind. Hence, Harry must learn Occlumency to put a stop to this. Snape puts some of his memories into Dumbledore's Pensieve before beginning the actual Ho Yay part. Snape uses his wand to penetrate Harry over and over again. Harry tries to resist, but Snape is just too much for him. Before long, Harry is on all fours. Okay seriously, Snape is using a spell to gain access to Harry's memories. Harry is supposed to be blocking him out mentally, but he's pretty bad at it, mostly because Snape is being a jerk about it. When Harry sees a memory of his arrival at the Ministry of Magic, he realizes the door he's been dreaming about is the door to the Department of Mysteries. Harry asks what's in the Department of Mysteries and Snape is as helpful as you'd expect.
After the session, Harry goes to the library to discuss this development with Ron and Hermione. They agree that the weapon Voldemort is after must be in the Department of Mysteries. The people who work in the Department of Mysteries are called "Unspeakables", but no one seems to know much about what they do. Hermione suggests this door must also be the door which Sturgis Podmore was trying to get through. As Harry heads off to bed, he's hit by a vision in which Voldemort is extremely happy. Harry goes to sleep feeling that his first Occlumency lesson has made his mind weaker rather than stronger.