Seeing the Weasleys looking so thoroughly miserable put Snape in an even better mood, enough that even the sting of the dog bite eased off considerably.
The twins were forever giving him grief as it was, so he'd taken the chance to lay into them properly before sending them back to the common room.
Once they'd gone, Snape told McGonagall about the specters he'd run into, and that was when the two of them realized they'd both encountered the exact same creatures.
Comparing notes, they came to the same conclusion: whatever those things were, they weren't Dementors. Dementors had physical bodies and couldn't pass through walls, while these things had been insubstantial, closer to actual ghosts.
"Whatever they were, something has clearly gotten into the castle. For the students' safety, I think we need to search the place thoroughly."
McGonagall put it to Snape directly.
Dumbledore had barely left Hogwarts before all this started, and it left her with a bad feeling, as if somewhere, unseen, a pair of eyes had been watching them all along.
"Fine. Go and alert the other staff. Get the castle's ghosts and portraits moving too, see if any of them noticed anything."
Snape had plenty on his own plate as it was. He had to keep an eye on Quirrell on one hand, and hunt down whoever was hiding in the shadows on the other, and on top of that there was still so much he hadn't worked out.
The parchment. Gandalf. A Balrog. A troll. And now Dementor-like specters.
He sighed, and the two of them went their separate ways to get started.
Altair, meanwhile, had already put the crystal away and settled in for a thoroughly satisfied night's sleep.
The House Cup was as good as won this year. A few dozen more points and the main quest would be as good as done. After that it was just a matter of racking up the score.
The next morning, Altair headed down to the Great Hall.
The mood inside was strange. Some students were still going over last night's troll incident, while others had picked up on something odd in the behavior of the castle's ghosts and portrait figures and were busy trading increasingly wild theories about it.
A cluster of Gryffindor's better students stood staring blankly at the jeweled hourglasses that kept the House Cup tally.
They could hardly believe it. In a single night, Gryffindor had lost a full three hundred points.
At this point they might as well announce Gryffindor's last place finish early.
Plenty of people had already guessed the twins were behind it, since they'd spent days getting ready for something on Halloween night. It looked like the twins' two year unbroken streak of never getting caught sneaking out had finally come to an end.
Altair ate his mashed potatoes with perfect composure, as though none of it had anything to do with him whatsoever.
Then Hermione showed up.
"I am going to lose my mind, Altair!"
She dropped down next to him without ceremony, shot a glare across the table at Pansy Parkinson, banged the table for a glass of milk, drained half of it in one go, and only then let out a long breath.
"I could scream! Last night Harry and Ron, and Ron's brothers, and some other third year Gryffindors, all snuck out, and Snape and McGonagall caught the lot of them red handed."
"Fifty points each! Gryffindor's going to end up with the worst House Cup score in history this year."
What Hermione was saying was more or less the consensus among the entire House by now.
In a normal year, when the Cup tally came due, all four Houses usually sat somewhere between three hundred and five hundred points. Gryffindor, thanks to Snape's endless excuses for docking points, usually hovered just above three hundred.
Now, counting what Hermione and the others had already lost before this, Gryffindor was sitting in negative numbers.
At this rate they might not even claw their way back to zero by the time the Cup was tallied.
"Don't dwell on it, you'll only make yourself miserable. None of it's your fault anyway."
Altair had to work to keep a straight face.
It really wasn't Hermione's fault. It was his.
"Oh, and have you heard anything? People are saying someone's gotten into the castle, some kind of enemy. It's all anyone's talking about."
Hermione grabbed some breakfast and kept talking between bites.
"They're saying whoever it is let the troll loose last night. Remember when Professor Snape was sick before? People think it might be the same group, that the professors thought they'd left but they never actually did, and they've been planning last night's troll thing the whole time."
"Ron says the only reason George and Fred got caught was because McGonagall was busy fighting off some Dementors when she found them. You know about Dementors? I read about them, they're some kind of..."
"But Harry thinks it was Snape. He says he saw Snape's leg was hurt last night, and he thinks that three headed dog bit him, and Snape only ran into him and Ron because he'd gone up to the fourth floor in the first place. Harry's convinced Snape was there to steal something."
Hermione rattled on, filling Altair in on everything she'd picked up around Gryffindor Tower, and he nodded along as he listened, which pleased her no end, since it meant Altair was actually taking in what she said.
"I don't know if there's real danger or not, but look at the ghosts, look at the portraits, they all seem so on edge lately. I feel like something big is about to happen."
"I mean, something as frightening as a Dementor showing up at Hogwarts. It's honestly hard to even wrap my head around."