Harry came back to the common room that evening with the barely-suppressed energy of someone sitting on news, and when he finally let it out — first-year on the Gryffindor team, first time in nearly a century — the room came apart with noise.
Kevin gave him a genuine smile and clapped him on the shoulder. "Congratulations. You looked completely natural up there."
"I didn't even think about it," Harry said, which was the most honest thing you could say about talent.
Ron was loudest. Hermione was warm in the careful way of someone who wanted to be pleased but was also privately calculating how Quidditch practice would affect Harry's study schedule. Kevin filed the observation away without comment.
"Hagrid's," Harry said. "We should celebrate. Come on — "
"Mr. Kevin."
The voice came from directly behind them. Everyone in the vicinity jumped.
Snape stood in the portrait hole entrance with the air of a man who had been waiting there long enough to make a point about patience.
"My office," he said. "Now."
He turned and walked. Kevin, after a beat, followed. He glanced back at Harry, Ron, and Hermione, who were all wearing the identical expression of people watching someone be escorted from the building.
"Go to Hagrid's," he said. "Don't wait up."
Snape's office contained, at a conservative estimate, eight hundred different things that needed doing. Herbs in various states of dryness covered every horizontal surface, jars and packages piled on the shelves, and a list waited on the central workbench — two pages, closely written, in Snape's hand.
The man himself was already gone by the time Kevin looked up from reading it.
Kevin surveyed the room for a long moment.
Mermaid scale powder. He checked the shelves. Whole scales in waxed paper packets. No powder.
Grind first, then.
The list wasn't punishment. He understood that within the first twenty minutes — it was demanding in the way that a textbook demands, each step connecting to something else, the annotations in the margins explaining why rather than just what. This was curriculum. Unorthodox, unpaid, and delivered entirely without warmth, but curriculum nonetheless.
Kevin allowed himself one moment of something approaching gratitude, directed at the absent ceiling, then picked up the grinding stone.
He worked. For the first hour it was simply labour — methodical, repetitive, his hands learning through repetition the specific pressures and motions that each ingredient required. Then it started to click, the way things did when practice finally caught up with understanding, and he found his rhythm.
At some point he started talking to the ingredients.
He wasn't entirely sure when this began. The unicorn horn was very smooth and the lamplight made it glow, and he mentioned this out loud, and from there things escalated in a direction he couldn't entirely account for. The giant bone received what he would later describe as an inappropriately enthusiastic greeting. The porcupine quills were assigned personality traits. He became genuinely excited about a particularly vivid interaction between dragon heart blood and blueheart grass and may have, briefly, addressed Voldemort directly.
Somewhere during all of this, Snape had applied a Silencing Charm to the door, which was the first indication Kevin had that anyone else was present.
He glanced at the door. The Silencing Charm was new.
Ah.
He grimaced, packed that memory somewhere he could cringe about it later, and returned to work with renewed focus and somewhat less commentary.
He missed dinner entirely. Missed curfew. Missed the point at which the corridors went quiet and the castle settled into its nighttime self.
He was on his fourteenth batch when the door opened again.
Harry, Ron, Hermione — looking guilty, holding bread and a flask of juice, wearing the expressions of people who had conducted a whispered debate about this for at least ten minutes before committing.
"We brought food — "
Kevin was mid-step and didn't look up.
They fell quiet. He finished what he was doing. Let the batch settle.
The potion cleared to amber-gold. Not almost-right, not close — there. Correct.
"Yes."
He straightened, hands going to his hips, head coming up. Grabbed the knife from the bench before the thought had fully formed, opened his palm, drank.
The wound healed in under a minute. The old cuts — the dozen small ones along his forearm from the earlier testing — smoothed over and vanished as the potion worked back through them. His hand was clean.
He laughed. It came out a little unhinged, which he acknowledged was understandable given the hour and the circumstances.
Hermione had gone very still. "Kevin," she said carefully. "Your hands."
"All fixed," he said, holding them up. "Look — gone. Completely healed. That's the point."
"There were so many cuts — "
"That's how you test a Healing Potion. Systematically." He was already packing up his notes, sorting vials, organising the bench. "The good news is it works. The bad news is I think Professor Snape may have been in this room at some point this evening."
"He was," Harry said. "He came to the door twice and — "
Kevin closed his eyes briefly. "Right."
He spotted the vial. 99 in familiar handwriting, standing on the bench in the lamplight.
He picked it up, looked at it for a moment, then tucked it carefully into his bag alongside his notes.
They were quiet in the corridors back to Gryffindor. Hermione walked beside him with the expression of someone who wanted to say several things and was choosing between them.
"You're not going to stop doing that, are you," she said finally. "The — the testing. On yourself."
"It's the most direct method."
"It's also the most alarming method."
"I'll be more discreet." He glanced at her. "Thank you for the bread."
She looked at him for another moment. Then, with the slight sigh of someone adjusting their expectations to match reality: "You need to sleep."
He did sleep. Ten hours, clean through, and woke up feeling like himself again.