Harry rather wished he hadn't agreed to attend Slughorn's party. Were it not for Luna, who was outrageously garbed and speculating about a Ministry conspiracy to spike the punch with some as-yet-unheard-of mind control agent -- in short, being her usual entertaining self -- he might have made his excuses and scuttled off an hour ago. In addition to avoiding the attentions of the host, the celebrity hangers-on, and various predatory girls (to which Hermione had alerted him just the other day), he found himself steering clear of both halves of the Hermione-McLaggen duo, who were easily the most dysfunctional couple in the room, which was saying something, at an affair such as this.

"Look at that witch's hat," said Luna, dragging his attention away from observing McLaggen from across the room.

The hat in question was an impossibly ancient-looking thing, with so many patches in mismatching colors that it was a wonder it didn't fall apart on the witch's head. It had probably been slathered with Reparos and Sticking Charms. It reminded Harry of Remus, the way he looked after a full moon -- or the first time Harry saw him, on the Hogwarts Express with his battered trunk.

"It looks a bit like the Sorting Hat, doesn't it?" Harry said.

"I suppose," said Luna. "You can tell it can't talk, though. I imagine it'd be happier if it could."

"Happier?"

Luna smiled. "It's old enough to have seen all sorts of interesting things, but it can't talk about them, so all anyone's ever going to think is that its witch should toss it in the bin. If it could talk, like the Sorting Hat, then people would probably keep it around."

"Err... I guess." Harry glanced away from Luna and spotted Snape, who appeared to be leaving the party with a shot of Firewhiskey in hand, resolutely ignoring Slughorn's gestures in his direction. Harry almost grinned at the sight; he wasn't at all surprised that Snape had no patience for the man -- he hardly did himself. Snape paused briefly in the doorway, downed the Firewhiskey, and dropped the glass deliberately at his side, where it disappeared with a pop and a faint shimmer of house elf magic. Of course, thought Harry, the party would be catered by the Hogwarts house elves. Won't Hermione be disappointed.

Hermione, for once, didn't notice. She was talking to some Ministry witch and had her back to McLaggen, who looked like he was contemplating ways to intrude on the conversation without making a complete fool of himself -- from across the room. Luna nodded at Harry and said, "She's a Gringotts liaison, I think. My father said they were looking for a way to turn onions into Sickles -- or Sickles into onions, I don't remember which."

"Right," said Harry distractedly. He had turned his attention back towards the doorway in time to see the hem of Snape's robe dart around the corner. That's odd, he found himself thinking, isn't his office in the other direction?

"Oh, no," said Luna. Harry turned to look. McLaggen was stomping away from Hermione in a huff, undoubtedly thinking himself more subtle in his anger than he actually was. Hermione looked like she was trying to hide behind her tiny plate of hors d'oeuvres, turning pink as she stammered out something -- an apology, or perhaps an explanation, Harry thought -- to the Ministry official.

"Right," Harry said, not looking at Luna. "Listen, I'm going to give McLaggen a piece of my mind -- don't mind if I leave you here for a bit, do you?"

Luna cocked her head. "You're not," she replied.

"What?"

"You're not going to talk to McLaggen. There's really no point. You want to know where Professor Snape's gone, I suppose."

"I -- what?" Harry stared at Luna, who was smiling serenely back at him. "No, I -- why would I care? Why would I care that he's gone off in the wrong direction?"

"It's all right not to trust people, Harry. And it's all right to trust them, too. You just have to sort out which is which."

Harry glanced at the doorway, and back at Luna. "I wonder how you do it, sometimes," he said, clapping her on the shoulder. "Thanks. For -- for coming tonight, and everything. I've got to go."

"All right, Harry. Watch out for the Blibbering Humdingers."

"And for Professor Snape. Not sure which is worse," said Harry with a grin. He made his way towards the door, muttering "Sorry, need the loo, got to go," as he elbowed past a trio of slightly tipsy witches. He dropped his plate and glass behind him, trailing a shimmer of house elf magic in his wake.

Harry strained to hear what they were saying; Malfoy was making a concerted effort to whisper, and Snape's voice had dropped an octave, into the soft, deceptively calm register that Harry associated with the man at his most dangerous. "I don't need your help!" Harry could make out, followed by a scrape of furniture. "I'm not a boy anymore. I'll prove myself to him -- I have to."

There was barely any warning before the door was violently thrown open; thankfully, it was hinged on the side opposite Harry. Malfoy stormed out of the room, his hands fisted in the pockets of his robes, the outline of his wand and knuckles pressed prominently against the cloth. Harry waited until he'd turned the corner, and then, gripping his own wand in his sleeve, stuffed his cloak into his robes and walked into the room.

"You're helping him," he said, drawing his wand.

Snape raised an eyebrow. "Eavesdropping, I see. I take it Draco didn't notice you?"

"I thought you were on our side!"

"I am." He twitched his wand at the door, which shut and locked itself with an audible click.

"But -- you're helping him! I heard you!"

"There seems to be an alarming gap between your powers of observation and comprehension, Potter."

"My what? I know what I heard. You're helping them -- the Death Eaters -- aren't you? You -- Dumbledore trusts you!"

"As he should. We are on the same side."

"No, we -- you lied! You -- I --"

"Potter! For once, shut your mouth and listen to me!" said Snape, stalking forward to stand directly in Harry's line of vision. "Cast your mind back to everything you know about me, about what I do, and for which master. Consider that there are appearances to maintain. Think! Who are Draco Malfoy's parents? Why might it be advantageous to convince him that I want to help him?" Snape paced away from him, his robes swirling behind him like a pool of ink. "The simplest answer is not always the correct one, Potter. But if you are willing to risk everything -- the whole war, the fate of the Wizarding World, everything we hold dear -- on your own flimsy hypothesis, then by all means, take whatever misguided vengeance you see fit." Snape turned, slowly, holding his arms away from his sides, his fingers spread and his palms empty. "Go on. I'll not stop you."

Harry held his wand remarkably steady, trained on Snape's head. A moment passed, and another, before he lowered his arm. "You fooled me, at first," he said softly, shrugging as he pocketed his wand.

"As I should have." Snape smirked. "If I did not manage to fool one obtuse Sixth Year, how do you think I survived being a spy for all this time?" More gravely, he continued, "You should know, I think, that appearances are often deceiving."

Harry scuffed a trainer along the ground. "Were you really going to let me kill you?"

"I knew you wouldn't. I'd heard about the incident at the Ministry. You didn't kill Bellatrix Lestrange -- couldn't even cast a proper Cruciatus on her."

"Still a risk. You didn't even have your wand."

"Wandless magic, Potter. I'm surprised you hadn't considered it."

"Against Avada, though?"

"Again, I don't believe Unforgivables are quite your forte. At worst, you'd have Stunned me and alerted the Headmaster," said Snape, "who would have promptly Enervated me and offered me one of those inane lemon drops. There is very little that happens within the walls of Hogwarts Castle that he does not know about, you must realize. And that includes this little scheme of Draco's, so I would put it out of your mind, if I were you."

"What is it?" asked Harry, now curious. "What's he doing?"

"It is really none of your business, now, is it?"

"But I --" Harry caught himself and said instead, "All right, then, I guess." After a moment's hesitation, he added, "Are you going back to Professor Slughorn's party?"

"No. I should think I've had enough inane social chatter for an evening."

Harry grinned. "Yeah. I went with Luna, though, so it wasn't that boring."

"Luna Lovegood?" Snape snorted. "Yes, I suppose she would be entertaining." He folded his arms, his hands disappearing into his voluminous robes, and said, "You are spending the holidays with the Weasleys, correct?"

"Err... yes. Why?"

"The Headmaster has placed certain protections on their residence, but even so, it is not as safe as Hogwarts or your aunt's house. You must Occlude at all times."

"I do."

"Even while asleep?"

Harry glanced at his shoes. "I try. I've had one or two of those weird dreams, but aside from those, I Occlude every night. They might not even be, you know, that kind of dream -- might just be nightmares."

"We've established, I thought, that by now you should be able to distinguish the two," Snape said impassively.

"Yeah, I know. Most of the time, I can tell -- I know that my nightmares are just normal dreams, usually. There's only been one or two that I wasn't sure about, really."

"At least you seem to be showing some improvement," said Snape. "Not at the rate I'd like, but it's certainly better than anything you did last year, for what little that's worth. Remember to Occlude at the Weasleys'. Read the books that Lupin supplied, if you aren't too preoccupied with stuffing yourself with sweets."

"Yes, sir," Harry replied, "I know. And -- happy Christmas, if I don't see you before we leave."

Snape inclined his head, the barest trace of a smile ghosting over his lips. "And you. You ought to return to the soirée, now -- I'm sure Miss Lovegood is waiting for you."

"You sure you don't want to come, sir?" Harry asked, grinning.

Snape snorted. "Really, I have better things to do. Go on," he said, making a shooing motion with his hand, "get out of my hair for the night."

"Right, got it," said Harry, as he shut the door softly behind him.