"Let's have another look at the Weasley twins."
The thought had barely formed before the image inside the crystal shifted again.
Say what you like, the Ithil-stone was ridiculously useful. Calling it a relic wouldn't be much of an exaggeration.
Over dinner, Hermione had mentioned that the Weasley twins were planning a night out, and dragging others along with them, dressed up as ghosts and ghouls to torment poor Mr. Filch.
If Altair didn't help get some points docked over this, it would be a waste of all the effort the twins had put in.
"Dock enough points this time, and even if Harry goes and kills Voldemort himself, Dumbledore still won't manage to put Gryffindor ahead of Slytherin."
Altair snickered.
The crystal showed him Gryffindor Tower.
"Hm? Why is it Hermione?"
He looked faintly embarrassed. The moment he'd thought of Gryffindor, Hermione had somehow been the first person to come to mind, and now the image had settled on her dormitory.
"Cute pajamas on this one... though isn't she going to catch a chill?"
He glanced at the fireplace in her room, decided he was overthinking it, and waved a hand. The image switched to the Weasley twins.
They were in the Gryffindor common room.
Unfortunately, not many people had actually agreed to come along.
The twins' idea had gotten plenty of takers at first, but after the troll business, most of them had lost their nerve.
In the end only two of the twins' third-year roommates were joining them, not a single second-year, and just Harry and Ron from first year.
Six in total.
"We made these specially for Halloween. Put the mask on and your whole body gets wrapped up in this black mist. You float along like a proper ghost."
George Weasley pulled the mask on over his face as he spoke.
Black mist billowed out at once, swallowing him whole, until nothing was left showing but the grinning, hideous mask.
"Ooh! I bet Mr. Filch is going to love this!"
The twins' roommates let out startled whoops of approval, and Harry and Ron traded a look, both equally stunned.
"Right, let's get moving then. Shame the rest of them will be missing out on all the fun."
Fred said it with something like genuine regret, and pulled on his own mask.
The other four followed suit, and in no time the common room held six roiling clouds of black mist, each one topped with a snarling ghost mask.
With the pumpkin lanterns casting their dim glow around them, the effect was genuinely unsettling.
"I want to go check the dungeons and the fourth floor while we're at it... something's off about tonight's troll. Might have to do with whatever Fluffy's guarding. I want to make sure Fluffy's still there."
Harry murmured this to Ron, who thought it over for a moment before nodding.
"All right, the two of us will go take a look in a bit."
George eased the portrait door open. The Fat Lady had already fallen asleep, and the six of them slipped out without a sound.
"George, Fred, we've got something else to take care of."
"Fair enough, fair enough. Shame you'll miss Filch making a fool of himself. Watch yourselves, don't get caught."
George added the warning; he and Fred had the Marauder's Map between them, so running into another professor wasn't much of a worry.
"We know."
Ron called back, and he and Harry headed off toward the fourth floor while George and the others made for wherever Filch was.
Watching the six clouds of mist scatter in different directions inside the crystal, Altair let out a low chuckle.
The twins had the Map, so he wouldn't be stepping in there himself. But...
He drew his wand and gave it a light flick.
"Lesser Undead Creation!"
"Summon Spectral Spirits!"
As he murmured the incantations, a dozen or so hideous specters flickered into being inside the dormitory.
They looked half real at best, drifting through the air and trailing thin ribbons of cold, close enough at a glance to pass for Dementors.
The fire in the hearth guttered wildly. In their beds, Malfoy and the others, still deep asleep, pulled their blankets tighter against a cold they couldn't explain.
"Off you go."
Altair steered the specters with his mind, and under his control they slipped straight through the walls, drifting down toward the castle's dungeons.
He kept his eyes fixed on the Ithil-stone, guiding them through it.
He sent a handful of the specters toward Snape's quarters first, and the rest toward McGonagall's. Since Harry and the twins had split up, it only made sense to fetch two professors instead of one.
McGonagall had been at her wit's end over the twins' pranks for ages, never quite able to catch them in the act. With a little help from Altair this time, she might just dock fifty points off each of them out of pure fury.
A few of the specters drifted silently into Snape's quarters.
Snape had only just gotten back. He'd bandaged the wound on his leg well enough for now and stood leaning against the wall, turning over the day's events in his mind.
He was certain of one thing: Quirrell was working for Voldemort.
Dumbledore seemed to know it too, though he clearly had something else in mind.
What left Snape feeling utterly useless was that someone else was hiding in this castle, and he didn't have the first clue who.