The Occlumency Draught experiment concluded cleanly.
No unstable compounds. No scorched batches. Ten vials, all viable, sitting in a neat row on Snape's workbench as the test mouse investigated its temporary new perspective on the world with the bewildered calm of an animal that doesn't understand what it's been given but has decided to be cautiously optimistic about it.
One in the morning. The underground workshop was dead quiet except for the scrape of Kevin's cloth against the worktop as he cleaned up.
He'd been building toward this for a week. He set down the cloth.
"Professor," he said, keeping his voice level, "I want to learn the Killing Curse."
Snape looked up. One eyebrow elevated slightly.
He didn't speak immediately. Kevin watched the calculation move behind his eyes — the rapid assessment of motivation, of risk, of what Kevin Croft wanting to learn Avada Kedavra actually meant in practice.
"I'm not trying to cast it on anyone," Kevin said. "What I want is the component that attacks the soul. The mechanism of it. Isolate that — strip out the lethal element and keep what actually reaches."
Snape set down his notes.
"Did Dumbledore tell you?" he said quietly.
Kevin blinked. "Tell me what?"
"Potter's situation."
The way he said it — flat, clipped, like a man pressing on a bruise he's spent years learning to ignore — told Kevin everything. He stayed still for a moment, running through the implications.
"No," he said. "I worked it out myself."
Snape studied him. Kevin didn't look away.
"You want a non-lethal soul strike," Snape said. "To excise the fragment in Potter without killing him."
"Yes."
Snape closed his eyes.
Kevin waited. He'd learned, over years of working with this man, that the silences were functional — they were the sound of Snape thinking rather than speaking, which he did in roughly the same proportions as most people did the reverse.
In that silence, Kevin could only imagine what was being weighed. He had, over the last several months, developed a reasonable model of what Snape knew about Harry's situation, and what that knowledge had cost him to carry.
"Come to the Forbidden Forest after dinner tomorrow," Snape said finally. "We'll begin."
Kevin felt the tension in his shoulders release. "Understood."
"And Kevin." Snape's voice had shifted — not softer, exactly, but with a particular weight. "What, precisely, do you know about the mechanics of the soul fragment? The specific conditions of its existence inside Potter?"
Kevin paused.
"Honestly? Not much beyond the basics." He scratched the back of his head. "I know it's there. I know the general circumstance of how it got there. Beyond that I've been extrapolating."
Snape stared at him with an expression that could have cured insomnia at fifty paces.
"You know nothing. And you've decided to develop a spell that targets the soul of a living person."
"I've got to start somewhere—"
"Are you genuinely attempting to kill Potter?"
Kevin opened his mouth. Closed it. "I mean, no, obviously—"
"Because that is what 'I'll figure out the soul mechanics as I go' describes."
Kevin squirmed under the weight of the stare. "That's... fair. Yes. I'll read more before we start."
The silence that followed had a texture to it — specifically, the texture of a very intelligent man reconsidering the wisdom of a bet he had just placed.
Three days later, Harry found Kevin's workroom occupied only by Hermione, who was reading with the focused serenity of someone who has claimed a space and intends to keep it.
"Where is he every evening?" Harry dropped into the armchair. "He disappears after dinner and doesn't come back until curfew."
"Research project with Professor Snape," Hermione said, without looking up. "He mentioned a new spell. Preparation for something ahead."
"Does he tell you what it is?"
"Not the specifics. But Snape is there, so he's not going to do anything genuinely reckless." She turned a page. "I trust him."
Harry absorbed this. "He also said he's skipping Slughorn's dinner tonight."
"He mentioned that too."
"Did he — could you tell Slughorn for me?"
Hermione finally looked up. "Tell him yourself."
"I don't want to go either."
"Then don't go."
"I have to go. Dumbledore essentially told me to."
"Then you're going and Kevin isn't and Slughorn will deal with it." She looked back at her book. "Good luck, Harry."
Harry stared at the side of her head.
"You're both abandoning me," he said.
"We're giving you room to develop the relationship independently," Hermione said. "It's tactically sound. You'll do much better without Kevin in the room — Slughorn won't treat you as an extension of someone else's network."
Harry thought about this. It didn't make him feel significantly better.
"That sounds like something Kevin said."
"He did say it. He was right."
Harry gave up and went to find his dress robes.
Deep in the Forbidden Forest, two weeks into the training sessions, the work was producing results that were less satisfying than the concept suggested.
The Killing Curse did what it did. Kevin had the magical capacity to cast it — that had never been the question. The question was what happened when you tried to isolate the soul-targeting mechanism from the lethal delivery system, and the answer, in practice, was: nothing good.
Avada Kedavra required genuine intent to kill. Not a performance of it. The actual thing. It was drawn from a very specific place inside the caster, and trying to access that wellspring and then redirect it before the spell completed was like trying to stop a struck match halfway through its arc.
Either it killed, or it failed. The middle ground Kevin was trying to build didn't exist yet.
He sat cross-legged on a tree root at midnight, looking at the evidence of the evening's work. The Acromantulas had been used rather than the forest's smaller creatures — partly because there were far too many of them, partly because their natural armour meant that unsuccessful attempts didn't result in instant death, and partly because Aragog's colony had already been pushed to the outer ranges and Kevin wasn't going anywhere near the inner territory.
The problem wasn't power. The problem was architecture.
Crack.
He looked up.
Gren Dore stood at the edge of the clearing with his arms folded, tilted slightly against a birch tree, watching Kevin with an expression of genuine intellectual curiosity.
"I wasn't sure it would be you," Dore said. "But I wasn't surprised."
"How did you find this spot?"
"I followed the green flashes from about half a mile out." He looked around at the Acromantula bodies on the ground. "You're not learning it. You're trying to take it apart."
Kevin said nothing.
Dore crossed to a nearby root and sat down with the ease of someone who has decided the conversation is interesting enough to stay for. "Durmstrang teaches exposure to Dark Magic, not mastery of it. But exposure is enough to learn what can't be done with it." He paused. "The Killing Curse can't be scaled. Can't be partial. The intent is the mechanism — you can't want to harm without wanting to kill without losing the spell entirely."
"I know," Kevin said.
"So you're after something else. Not the spell as it stands. The component underneath it." Dore studied him. "The touch of it on the soul."
Kevin looked at him steadily. "And?"
"And you can't get there by weakening the spell. That just gives you a failed Killing Curse." Dore's tone was matter-of-fact, not unkind. "But you might get there by going in from the other direction entirely. Soul magic isn't only destructive. Horcruxes pull from the same principle — the soul can be separated from a living person without death. The mechanics exist. They're just not attached to this particular curse."
The night was very quiet.
Kevin turned the idea over. He'd been so focused on the Killing Curse as the starting point — find the component, isolate it, redirect it — that he'd been trying to modify a weapon rather than build a tool. The Horcrux framework was different. The soul division in Horcrux creation was an act performed by the maker on themselves, but the underlying principle — that a soul could be separated from its host without destroying either — was exactly what he needed.
Different direction. Same destination.
He felt something shift in his thinking, the specific sensation of a framework becoming suddenly more useful.
"Thanks, Dore," he said.
"Grin," Dore said pleasantly.
"Dore," Kevin said, without heat.
Dore smiled. "I'll take it."
"How do you know about Horcruxes?"
Dore glanced at the sky. "Same way most people know things they probably shouldn't. People who cared about me told me what they knew, and I listened."
"That's not an answer."
"It's the answer I've got for tonight." He stood, brushed bark from his robes. "You should head back. Curfew's been over for an hour."
Kevin looked at the cleared space around him. Then at Dore.
He thought about Dumbledore's instruction: give him the latitude you'd give any student. He thought about the fact that Dore had, twice now, wandered into dangerous situations and chosen to be useful rather than threatening. He thought about the specific quality of intelligence Dore carried — not the performance of it, but the real kind, the kind that noticed things and filed them and spoke when speaking served a purpose.
"Want a lift back?" he asked.
"I'll manage. Go."
Kevin went.