By evening Severus had come round properly. Madam Pomfrey checked him over, pronounced him fit, and he made his way down through the castle to the dungeons.
He reached the skull-carved stretch of wall, said "Pure-blood," and waited for it to slide open.
The common room had been in the middle of the usual evening noise. The moment he walked in, it quieted, and a dozen faces turned toward him with something that looked, unexpectedly, like approval.
"Here he is," called a cheerful voice. The house prefect came forward: Macmillan, the same boy who'd backed him up in front of Slughorn.
"Did I miss something?" Severus raised an eyebrow.
"Don't play innocent. A hundred points off Gryffindor in two days. That's not a thing many people manage." Several of the other Slytherins nodded along.
"Glad it helped." He moved straight toward the dormitories. "I'm done for today. Anyone who wants to talk, I'll be in my room."
The look that rippled around the common room at that was not warm. These were not people who took well to being brushed off. Macmillan said nothing. He simply said good night and went about his business, which was exactly the right response, because he knew considerably more than the others about where Severus had actually spent the day. He also understood that making himself pleasant now, while the others were busy putting Severus's back up, was the most sensible possible investment. Severus was interesting, and not only for the Potions gift, though that was real enough. From their very first meeting, Macmillan had felt it: something had changed in the boy. The quiet, battered quality was gone, replaced by something he couldn't quite name but very much wanted to understand. This was Macmillan's last year at Hogwarts. If he didn't build something with Severus now, he wouldn't get another opportunity. That was the thinking behind the politeness, the patience, the careful lack of pressure.
Severus closed his bedroom door, ran a swift check for surveillance charms, and then collapsed face-down onto the bed.
"Another one done." He rolled over, pointed at the nightstand, and an inkwell, a quill, and a blank sheet of parchment floated out. I'm going to need some outside help with this next part.
The quill scratched away for a few minutes, then stopped. The sheet rolled itself into a scroll.
"Need an owl." The location of the owlery surfaced immediately: west wing, upper floors. Convenient. He opened the nightstand drawer and pulled out a small pouch that jingled softly. Ten Galleons and seven Sickles rolled onto the bed. "Not exactly flush. Money's going to be a problem." He extended one hand. "Fotia." A small sphere of fire bloomed in his palm, warm and obedient. "One word, and I've got fire. And the runes from home work here, which is something. Still not enough until I've built up the core and taken that potion. I need to reach at least Magister level before I can feel reasonably safe, and then I can work on everything else somewhere quiet, away from whatever this war is turning into." He yawned and closed his eyes, then snapped them open again. "Wait." He sat up. "That could actually work. If the runes function here, then... I'll need materials, but there's a forest right on the grounds."
He turned the plan over for a while, decided it was sound, and committed to the next evening as his start point. The rest of that day went to the library: the full castle layout, current against old, whatever the general stacks would give him.
Most interestingly, the oldest blueprints he could find anywhere in the library, even after going through every shelf under Madam Pince's long-suffering watch, dated to 1780. Nothing earlier. That was disappointing at first glance, and then rather pleasing. Things don't simply disappear from a school archive that size. Someone had made a deliberate choice to remove them.
The water and sewage plans were the same: 1780 and nothing before.
Still, you couldn't hide everything. Blueprints were only one kind of record.
In a historical text he found a brief note about a Corvinus Darke, surname Gaunt in parentheses, who had been responsible for installing the Hogwarts plumbing system in 1750.
Taken alone, unremarkable. Taken with the knowledge that the Darkes were descended from Salazar Slytherin himself: peculiar. Severus knew exactly how pure-blood aristocrats thought about manual labour. Suggest to any Slytherin student that they spend their time digging channels and laying pipe, and they'd look at you as though you'd said something offensive. Yet Darke, a man of that lineage, had apparently done exactly that, without any apparent objection, in what amounted to a glorified sewer. The absurdity was the point. No one would choose to do that without a reason, and the reason wasn't the plumbing.
Severus hadn't found anything concrete. He felt, nonetheless, that he was standing on the right ground.
Evening came, and he left the library. He had taken perhaps two steps when he stopped.
Sitting in the middle of the corridor, regarding him with cool, measured hostility, was a grey cat with dark tabby markings. It had drawn itself up to its full height and was watching him with the focused wariness of an animal that had decided he was probably a problem.
Severus smiled. The cat's fur stood on end.
At almost exactly the same moment, as though some instinct had fired, an elderly man came around the far corner at a pace that would have done credit to someone thirty years younger. His face was deeply lined and permanently set into an expression of aggrieved suspicion. His pale eyes moved in quick, calculating sweeps, clocking everything. Students scattered out of his path as he passed them. When the yowling reached him, his expression curdled, and he was already running.
He rounded the last corner and found Severus standing in the corridor with Miss Norris cradled in his arms, purring loudly.
"PUT HER DOWN THIS INSTANT!"
"She belongs to you?" Severus looked up with a pleasant expression, one hand moving in slow, even strokes along the cat's spine. "Miss Norris. That's a good name." He nodded at Filch in a courteous way. "Could I hold her just a little longer?"
"Miss Norris." Filch's voice had dropped an octave. Miss Norris gave a lazy, deeply contented meow and flicked her tail.
Filch stared. He was clearly trying to work himself back up to outrage and finding it difficult. He had just drawn himself up to say something cutting when Severus said:
"You take exceptional care of her. It's genuinely rare to see it done this well. The coat's healthy all the way through: soft, clean, good sheen. Eyes clear, no cloudiness, no discharge. She's alert and well-proportioned." He paused. "There's one small thing I'd want to look at, though."
"What?" All the hostility had gone out of Filch's face, replaced by something raw and worried. He leaned in toward Miss Norris, as if proximity would reveal the problem.
"Nothing urgent." Severus poked her gently on the nose. She opened her mouth just slightly. "That faint off-note in the smell. You probably caught it."
Filch sniffed. He nodded slowly and solemnly.
"Just a slight dietary imbalance. Easy to correct." Severus held out a hand, and Filch, without apparently deciding to, passed over the sheet of paper he'd been jotting notes on. Severus flipped it over and wrote out a balanced dietary plan for cats on the back. His father had been particular about cats, had made Severus learn everything there was to know about them whether he wanted to or not, though in truth he'd never minded. "Don't let her overeat. It won't end well."
Miss Norris expressed an opinion on this in no uncertain terms. Severus stroked the top of her head with a warm smile.
"Play with her properly, regularly. She needs your attention as much as anything else."
"Right. Yes." Filch was taking down every word. He took the sheet back, folded it with a care bordering on reverence, and tucked it into the inside pocket of his jacket as though it were something valuable.
"I won't keep you." Severus passed Miss Norris back to him and walked away.
Filch stood in the corridor for a full minute staring after the boy. Then it landed.
"He ran rings around me."
Miss Norris purred.
Filch looked down at her, and the sour lines of his face went soft.
"Fine. Didn't see a thing tonight. Come on, Miss Norris, there are four others still to catch." He grinned in a way that didn't bode well for anyone, set her down, and she vanished around the corner with an ominous chirp. Filch followed.
At the same moment, on the other side of the castle, Severus stepped out through a ground-floor door and crossed the darkening grounds toward a large solitary tree.
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