They sat with the quiet for a moment, the private joke settling comfortably between them in the empty classroom.
Then Harry's face changed. The ease went out of it, and what was left turned toward the thing that had been waiting under the whole conversation.
"Do you think it will come to a war?"
"I do not know." Arthur said it plainly. "I tried to head it off years ago. Spent a long time getting Amelia and Fury to work in the same direction, magical side and mundane side pulling together before the wall ever came down. It did not take." He shrugged. "So now I do the same thing everyone else does. I wait, and I watch."
"You not having an answer is its own kind of worrying."
"Or we are both worrying too much." Arthur let it go, easily, the way you set down a thing too heavy to hold in the middle of a good conversation. "Where are Amelia and Sirius, anyway. It has been a while since I heard from either of them."
Harry softened. He reached behind the desk and slid a postcard across, grinning despite the long day. "Sirius sent this. From somewhere with an alphabet I can't read."
Arthur turned it over. On the front, a harbour town drowning in sunlight. On the back, in a hand that had never once respected the space provided, Sirius had crammed a week of small Muggle adventures, and a single line at the bottom about Amelia sleeping past dawn for the first time in twenty years.
"Good," Arthur said, and meant it. "She gave that office more than it ever gave back. Let her sleep till noon for a decade."
"They asked me to bring Susan and come with them. Sirius said the wizarding world could run itself into the sea without me." Harry set the card upright, looking at the little sunlit harbour. "I said no."
"Why?"
Harry nodded at the rows of empty desks. At the cracked-and-mended floor. At the whole quiet, doomed, ancient castle around them.
"Because someone has to stay here and teach them how to duck," Harry said softly. "And the people at the top right now absolutely will not."
"Someone grew up into quite the protector." Arthur's mouth curved. "Let us see whether you have the power to back it up. How is the other homework coming."
Harry's whole demeanor changed instantly. The weary professor went somewhere else, and what was left was a man standing in front of an impossible teacher.
"It is agony," he admitted. "The hardest thing I have ever tried to do."
"Show me."
Harry laid the ash staff on the desk and stepped away from it, putting real distance between himself and the crutch. He stood in the centre of the empty room and shut his eyes.
Arthur watched with a flat, clinical patience.
Harry stopped reaching inward for the warm, faithful core that had carried him his whole life. He reached outward instead. For the cold of the ancient stone. For the old hum of the earth under the foundations. For the patient, ambient magic that had been soaking into this castle since before the first word of the first spell was ever spoken.
For a long minute, nothing.
"Stop ordering it, Harry," Arthur said quietly. "It is not a wand spell. It will never obey your voice. You ask it to agree with you."
Harry breathed out. Tried again. He opened his eyes and fixed them on a single stray quill abandoned on a student's desk.
He did not point. He did not speak. He simply looked, and poured every scrap of himself into one clean, wordless intent.
Lift.
The air in the room went heavy. Arthur felt the ambient magic shift, sluggish and clumsy as a glacier, and begin to move.
The quill twitched.
A thin line of blood ran from Harry's nose to his lip. His hands shook at his sides. His eyes did not leave the desk.
The quill rose. One inch. No more. It hung there, trembling against the whole weight of the world, held up by nothing but a man's refusal to let it fall.
He held it three seconds. Then his eyes rolled back and he went down.
Arthur crossed the room in a streak of silver and caught him before the stone could. He lowered Harry gently. The quill dropped back to the desk with a small, final clack.
Harry gasped like a drowning man surfacing, and wiped the blood from his lip with a shaking hand.
"I got it," he wheezed, a weak and triumphant grin breaking through. "Highest I have held it yet."
Arthur looked down at the strongest wizard alive save himself, who had just spent every ounce of his body and mind to lift a feather one inch off a desk.
By any sane measure, it looked pathetic. But Arthur knew it was anything but.
Harry had touched Ancient Magic maybe once or twice before, by accident, in the worst, most desperate moments of his life. Reaching it on purpose, and bending it to his will, had taken Arthur far, far longer than this when he first started. Harry was fast. Frighteningly fast.
"That was beautifully done, Harry." Arthur praised softly.
"Felt like lifting a mountain with my teeth." "Felt exactly like lifting a mountain with my teeth,"
"Because you're growing muscles you weren't born with. Your body is learning to carry a current it was never meant to hold." Arthur eased him up to sit against the desk. "But the door's open now. The hardest part is behind you. The rest is only repetition and stubbornness, and you have never once been short on stubbornness."
He stood, glanced at the three cracked flagstones, and passed a hand through the air. The stone knitted itself smooth, whole again, as though the lesson had never happened.
"Master the quill," Arthur instructed. "Lift it every day until it bores you. Do not reach for anything heavier until you can do it without painting the floor."
"You do know you are talking to the finest Defence Against the Dark Arts professor Hogwarts has seen in decades, right? I know the drill, Hayes."
"The finest in decades." Arthur considered it. "That is really not much of a bar to clear, is it? Half of them tried to kill you."
"You…" Harry pointed a shaking finger. Arthur only smiled wider.
They worked the stubborn quill a while longer. It came a little easier each grueling time, and bled just a little less. It was progress, and they knew better than to say so out loud and jinx it.
When Arthur finally rose to leave, Harry stopped him at the door.
"Can I ask you something, and get the honest version?"
"Always."
"What happens next out there?"
Arthur was quiet for a long moment. "I don't know."
"That's twice today you've said that."
"Because it's twice true." He leaned back against the empty desks. "I'm hoping the sane ones win. That somewhere on both sides there are enough people who'd rather be frightened of each other than dead, and that they're the ones still in the room when it matters. That's the whole of my plan now. Hope, and keeping my hands off it."
"And if the sane ones lose?"
"Then it's a war. A bad one. The kind nobody on either side is ready for." He said it without weight, which was worse than weight.
Harry nodded slowly. "Then here's the next question." He met Arthur's eyes. "Which side do you fight on?"
"None of them."
It came out flat and immediate.
"You," Harry said. "A Muggle born. The most powerful man in the world. They are about to tear the whole thing in half, and you will stand in the middle of it and lift a finger for nobody."
"For nobody." Arthur did not look away. "The moment I pick a side, that side wins. Not because they were right. Because I was holding the scale. That is not peace, Harry. It is my fist ending the argument, and everyone too afraid of me to say otherwise." He shook his head. "I will not be the reason one half of the world kneels to the other. I would sooner let them break it themselves than mend it like that."
Harry took that in. Then Arthur turned the question around.
"What about you? You don't get to shrug the way I do." He nodded at the staff. "You're the strongest wizard alive after me, and you're the only one who actually understands the other side. You know what their weapons do. The rest of them think a jet is a loud dragon they can Confund. If it comes to war, you walking onto a field could decide which way it tips. Both sides know that. So. What do you do?"
Harry was quiet for a while. He turned the ash-wood staff slowly in his hands, the way a man turns a problem he hasn't solved.
"I don't know," he admitted. "And I've thought about it more than I'd like." He looked up. "I don't like wars, Arthur. I've had enough of them for three lifetimes. I've watched people die standing behind me because I let them stand there. I don't want a banner. I don't want a side." A tired breath. "What I want is to keep this castle standing. Whatever the adults out there are screaming about, the children inside these walls get to grow up. Muggle-born, pureblood, doesn't matter. They come here frightened, and they leave able to survive whatever the world's become by then."
"Dumbledore would be proud."
Harry's face soured. "Do not." Then, slower, the anger going out of it. "Though the older I get, the more of his choices start to make a terrible kind of sense. All except the one where he raised me to die on schedule." He set the staff against his shoulder. "Arthur. The day I start seeing a student as a piece on a board, I want you to come up here and stop me."
"I will," Arthur promised. "So you really won't fight?"
"I did not say that." Harry's eyes were steady and there was nothing soft in them. "I said not today. With things the way they are, no. There's no side worth bleeding for. A Ministry the old families are dragging backward on one hand, muggle radicals who want the whole veil torn down on the other, and not one person at the top I'd cross a room for."
A heavy pause.
"But that can change. Fast. If Amelia and Sirius come home and take the helm. If saner hands end up on the reins than the ones holding them now. My answer isn't a principle, Arthur. It's a reading of the room. And I won't tie my own hands for a room that could empty out by spring."
Arthur looked at him. Bloodied. Bone-tired. Standing alone in an empty classroom he had quietly decided to hold against the whole coming century. Not for a side. Not for a strategy. For the frightened children other people would send him when the world stopped being safe.
He was not a soldier. He was not a weapon.
He was a door. Open to anyone small enough to need shelter, and shut to whatever came for them.
"They are lucky to have you, Harry," Arthur said softly. "Every last frightened one of them."
As Arthur turned his back to Apparate away, he paused and looked over his shoulder.
"Keep lifting the quill, Professor. The world can wait until you've stopped bleeding all over the floor."
And then he was gone.
Harry Potter turned back to the desk, alone in a castle far older than the quarrel out past its windows, and bent once more to the slow, bleeding work of lifting a quill.