Harry's first instinct was to Ask Hermione, but one look at her told him that she hadn't ever heard of this.
And that made asking her a really bad idea.
Not knowing things was stressful for Hermione, and when stressed, she tended to snap.
"I'm going to the library," Hermione said, standing up, even though she wasn't half done with her dinner. Harry didn't need to look to know Malfoy would be smirking across the room from them. If asked, Malfoy'd probably serve up some sort of ill-mannered quip, too. Harry's eyes flicked to the Ravenclaw table, but they were too far away to be heard, and the Hufflepuffs were all cuddled together like some sort of squirming pack of still-blind puppies - cute, but no good for eavesdropping.
Harry's eyes flicked up to the High Table, and he saw Snape stand. Parvati had started to say, "In Scandinavia, there's a legend..."
Harry let her words fade into the background - he couldn't stay.
He had detention.*
Harry didn't trudge down the stairs to detention. He walked, lightly, trying to make his footsteps quieter. That worked until he stumbled, hitting his shoulder on a piece of platemail. "Ow," he said, continuing downstairs.
"Enter," Snape said as Potter knocked on the door.
Harry knew, from the moment he stepped in the door, that this detention was going to be different than most. For one thing, there were no cauldrons. For another, the floorspace was entirely clear.
Harry swallowed a gulp, not entirely anticipating this.
This was a Defense detention, and so he'd better be prepared. It was almost like his armhairs standing on end, the way he focused. Ready, waiting, prepared to lunge, or roll, or even cast a spell.
Snape's wand moved, and Harry ducked into a roll - going on muscle memory, which was less instinct than intent.
It might have been fifteen minutes, it might have been four hours. Harry came out of 'battle-mode' as if coming out of a trance, with no idea of how long he'd been in it. He was sore, and Snape's wand was pressing into his throat, as Snape growled out, "Yield."
"I yield, sir." Harry said, trying (and failing) to control his gasps for breath.
Snape stood, putting his hands behind his back, before speaking, "The rest of the night is yours to enjoy."
"Thank you, sir." Harry said. And stood there, because he did want to know...
"Is there some reason you aren't leaving, Potter?" Snape asked, and he never seemed so snakey as when he was asking a question like that.
"What did you say to McGonagall at dinner?" Harry asked, just deciding to spit it out.
Snape started, "Well, we were discussing the merits of the Quiddich teams, specifically, dissecting the Ravenclaw team's weaknesses and strengths."
Great. That wasn't at all what Harry had wanted to know.
Snape picked that up straight off Harry's face, of course. "With regards to Lussi? I reminded her that the rules against flying broomsticks inside the castle were designed to prevent children from battering each other down, and that it was hardly appropriate to apply that to a child's training broom."
"Thank you, sir," Harry left as gracefully as he could - because he ached. He hadn't even thought of how odd it was that Luna had been on a broom. Of course, McGonagall had wanted to say something about it. However, the wonder was that Snape had disagreed. There was something here Harry was missing.
Walking up towards Gryffindor Tower was a weird experience, but it took a while for him to even notice how weird it was. It was after dinner, and there was no one around.
That wasn't unusual when you were in the dungeons. Harry knew the Slytherin Common Room was cozy enough (if prim and proper to the nines), but most of the dungeon was drafty and chilly. It wasn't surprising that even the Slytherins thought twice before spending copious time in essentially unused classrooms and dusty jumped-up storage closets.
Going through the main floors of Hogwarts, though, had Harry feel a tendril of unease sliding up and down his spine.
Where was everyone?
It was like the entire castle had been kidnapped.
Instead of going towards Gryffindor, and bed, like any sensible student would do after a detention with Snape, Harry's feet turned towards the library. There were few things indeed that would get all the Ravenclaws out of the library - and yet, as he didn't see a single soul on his way to the library, that twisting unease fought against his mind - trying to turn to dread.
Pince was in the library, sitting at her desk. Harry sighed with relief. He wasn't sure he could have taken it if everyone had been kidnapped by Aliens.
Or Death Eaters.
Harry wasn't sure which was worse - he knew he could at least find Death Eaters, even if they were horrible cowards that hid behind unplottable wards.
"Where is everyone?" he asked the librarian.
She shrugged, "Not in the library."
Harry would have turned to leave, except that he saw a flicker of bright blonde hair.
Luna? He thought, softly striding over towards her.
[a/n: Snape's not actually cruel enough to crucify Potter on Harry's own curiosity.]