He carefully counts the diamond-shaped panes in the window, running his finger around the lead outline of each pane before he adds it to his tally, saying each number out loud because there is a comfort in their logic and continuity. He comes to the same total as yesterday and nods, relieved. The world has not changed on him overnight, and that is good. That is reassuring.

The window dealt with, he turns to the wall, counting the stones, placing his finger in the exact centre of each stone with a precision that only someone with a ruler could possibly better. The numbers build up on his tongue as he methodically moves down the wall, counting. And there are as many stones as yesterday and he heaves a sigh of relief. It's always hard to go to sleep, knowing that the stones could so easily shift and vanish when his eyes are closed. If he's not there to keep an eye on it, the world could change without him knowing. It's better to be awake and know that everything is how it should be. He doesn't like sleeping but he knows he has to. Still, it's good that nothing's changed.

Counting done, he can turn back to his room, go past his bed and sit at the table where his breakfast waits patiently for him. Two eggs, one strip of bacon, and one piece of toast. Just as it should be, just as yesterday. That's good, he's pleased. And the house elf has put it on the plate symmetrically, so he can eat it. He can't eat it when it's not symmetrical, that just doesn't work. It's all wrong then and he can't eat it because if it looks wrong then maybe it will taste wrong – or maybe it will be wrong, it could be poison and if he eats it he could get really sick and if he gets sick then he might die and if he dies then—

But it doesn't look wrong. It looks just right. So it's okay and he can eat it. So he does, carefully and neatly, counting the number of times he chews because if he doesn't chew his food enough then maybe it will choke him and choking would be as bad as poison and he doesn't want to choke, he doesn't want to die.

There is a knock at the door and he tenses. Three knocks, at precise intervals, and he relaxes. Three is a good number because it has balance, and the steady rhythm of the knocking is reassuring. He doesn't like irregular beats. "Come in," he says, touching the wand in its holster on his wrist just to make sure, even though no one could take it without him noticing. But it's better to be sure, it's always better to be sure. If he assumes and he's wrong then maybe that could get him killed. Better to be safe. He likes to be safe. He's never safe.

"It's me." Harry shuts the door behind him and stands in front of it. "How are you?"

"Really you?" he checks. There's always Polyjuice. Or maybe glamour charms.

"Really me. I swear on Hermione's time turner."

"Very well." Only Harry would know to say that on a date that is a Tuesday and an even number. Unless someone used Legilimency. How would he know if someone had used Legilimency? Or Veritaserum? Or even the Imperius? There's no way to be sure it's really Harry and if it's an intruder then it can't be anyone who means him any good and that means he's in danger and he doesn't want—

"Expectro Patronum!"

The silver stag dances around the room and then nuzzles up to him, wrapping him in warmth and reassurance like a burst of phoenix song. This is Harry. It really is. Everything's all right. He wraps his arms around the stag's neck and buries his face in its warm side. Harry's magic warms him and tells him he's safe – and for a moment, one stolen breath out of time, he can believe it's true. It won't last, and too soon he'll be back to worrying about walls and Polyjuice, but here and now he can believe.

Harry stays on the other side of the room because Harry knows that he doesn't like having anyone near him. People who get close to you hurt you. It's better to stay away. He knows that. He doesn't want to be hurt. He just wants to stay here with the Patronus and be safe.

"Severus?" He looks up and the Patronus fades away. Severus. That's him. Severus Snape. He doesn't really remember much of being Severus Snape but he knows that's who he is. Who he was. Before the magic and the hiding and the bad-bad-bad changes. "Are you okay?"

"I finished the book," he says.

"That's good," Harry says. "Do you want me to bring you another one?"

He considers it. It's dangerous to have things brought in from outside. And sometimes books are ugly and unsymmetrical and they don't look right. Things that don't look right are bad. But books hold knowledge and knowledge is important. It's dangerous not to know things. Maybe more dangerous than to have things brought in. Not knowing things can get you killed and he doesn't want to die. "I would like another book," he says into the silence.

"Then I'll get you one."

"Yes." Harry's robe has settled crooked. Severus tries to ignore it, but the knowledge won't go away and it itches at him, hurting him to know that it's there.

"Severus?" Harry asks gently.

He can't ignore it. He can't. So he walks across the room (eight, evenly-paced steps) and carefully adjusts the fabric so that it sits right. That's better. It doesn't scrape across his nerves when it sits straight and the nagging feeling is gone from his brain and he feels like everything's okay now. Harry watches him gravely through his glasses. Severus stares back at him. They're the same height. He remembers Harry being shorter than him but this is better because they're just the same height and that is nice and neat and orderly. Things should be the same size, they match better then. But there's that scar on Harry's forehead, faint so that he couldn't see it from a distance but from this close he can see it and it's crooked and uneven and wrong. He doesn't like things that are wrong. They hurt him.

"I want it to go away," he says.

"What?"

"The scar."

"It's almost gone," Harry offers.

"But it's there. Make it go away."

"I can't."

Severus turns hastily, his fingers twitching at his sides. "It needs to go away. It's all wrong."

There's a quietly spoken spell behind him and he spins, wary. Magic he can't see is bad. He knows magic is bad. But the scar is gone. The scar is gone and that is better to look at. Undamaged skin, like it should be. But...

"It's still there."

"I know."

"It's not really gone."

Harry sighs. "No, it's only a glamour. But you can't see it, right?"

"But it's still there." He doesn't like it even if he can't see it. It's still wrong even when he only knows it's there. And he doesn't like things being hidden. Things being hidden is bad. Hiding is why he's here, counting his world to keep it in place.

"I know."

Severus presses the heels of his hands to his temples. "Can't you make it go away? It needs to go away." He rocks back and forth slightly, trying to fight the need to tear off the scar. He knows that Harry wouldn't like that but he knows that the scar is wrong. It's ugly and unsymmetrical and it's wrong.

"Sorry. I wish I could. Look, I could just go away—"

"No!" Severus panics, clutching at his wand and pointing it blindly around the room at unseen invaders while the fear takes away his vision so that all he sees in panicked blurs of colour. "You said you'd stay! You promised! He's coming and you have to stay! You said! You can't—"

"I'll stay," Harry says hastily. "I said I would and I will." He's not stupid and he doesn't try to touch Severus. "I'll stay."

Somehow he gets a grip on the panic and the phantoms stop blurring his eyes. He looks around worriedly, wondering what changed when he couldn't see straight. Did the window change? Did the door move?

"I was watching," Harry says. "Nothing moved."

Severus still takes a wary survey of the room. It looks okay. He thinks it's okay. Nothing's changed, he tells himself. Nothing changed. He's shaking with the effort of not counting the window panes again, convulsively gripping his hands into fists to fight the urge. Because he knows it's not normal, he knows it's not right. Normal people don't live with these worries, normal people aren't afraid all the time, normal people can leave this room and get on with their lives.

"Just count them," Harry says. "It'll make you feel better."

"It's not right," he manages to say between gritted teeth. "It's not good."

"It makes you feel better. That's good. Don't listen to them, okay? As long as it helps you it doesn't matter how stupid they think it is. Severus, just count them."

So he counts them, he counts the panes of the window, tracing the leaden outlines of the diamonds and reassuring himself that the world is the same as he thought it was, that it hasn't changed on him. Everything's the same. It's all right, really it is.

He sighs with relief, lightheaded with reaction, and sits down on his bed. His carefully-made bed, every corner crisp and perfect, every line of blanket ruler-straight. A sixteen-year-old boy shouldn't make a nice and tidy bed like that, he knows, but he can't not make it. He has to make it as perfectly straight and tidy as possible because crooked lines and messes are wrong and wrong things hurt. Everything has to be perfect, and so he carefully straightens the blanket where it creased a little when he sat down and then when he's satisfied he looks up and Harry's still there, watching him. Waiting. Patient.

"Why do you do that?"

"Do what?" Harry blinks at him in genuine confusion, the light glinting off his glasses and shading his eyes.

"Believe me. Let me be like this." He knows that how he is is wrong. But he can't change it. He tries, but he can't change it. Not even when they look at him. "They think I'm just making it up. They think it isn't real. They think..." He hates half-finished sentences because there is an ugliness to their unfinished nature but he doesn't want to finish that sentence either. Not even in his head.

Harry gives a half-shrug. Severus winces at the asymmetry. "I wasn't brought up magic," he says. "Wizards hate infirmity because normally nothing bad stays happened when there's magic, you're either dead or fine. But Muggles aren't used to quick fixes and they know that minds get sick too. They know that sometimes things don't heal."

"I try to get better." He sounds plaintive and his voice hitches in the middle, interrupting the smooth flow of the words in a way that hurts his ears.

"I know."

"But why do you stay?" That's the key, isn't it? He knows he's annoying and frustrating and troublesome. He can't help it, can't stop himself, but he knows very well that that is what he is. And why, of anyone, should Harry Potter stay here with him and visit him every day and put up with everything?

"You saved my life."

"We saved each other's." He doesn't remember an awful lot, but he does remember being at Harry's side when the other boy took down Voldemort, before he was the other boy. When he took a curse intended for Harry to give him the chance make the final shot. When Harry dragged him, bleeding and dying, off the final battlefield and got him to help. That time they could fix him, he remembers that.

And he remembers going before the Wizengamot on trial as a Death Eater and being sentenced to life in Azkaban. He doesn't remember going to Azkaban, but he remembers being broken out. He remembers trying to run far away because he didn't care if that made him an escaped convict, he just wanted to find somewhere very far away where he could stay alive. He'd just wanted to live. Only someone else had another idea.

The cheerful knock on the door has little rhythm and no evenness. Seven knocks, he counts automatically, and seven is a bad number because there's no symmetry to it, no beauty. Seven is an odd number, an ugly number. He instinctively raps his foot on the floor to make an eighth beat but nothing can make that knocking rhythmic and so he shakes his head violently to try and make the sound go away, gripping his wand in his hand because nothing that follows that sound can possibly be good.

Harry swiftly steps away from the door and though his wand isn't out his back is straight and his head is high and he stands near Severus, facing the door, as if they can face the intruder together. Together, with their matching heights and their matching hair and their matching skin. Pale and thin and dark-haired, they could be brothers, and the symmetry of it eases Severus's jumping thoughts. Symmetry is good. And having Harry nearby is good too. There's not a lot of safety in the world but there is safety in Harry.

Severus stands up even as the door opens, the knocker not waiting for an answer but just coming in – which offends Severus's sensibilities. A question should be followed by an answer, that is the way of things. A knock should be followed by an invitation. Otherwise the world gets all out of order and things are messy. He doesn't like messy. Which is why he doesn't look at the door, but carefully smoothes out the rumples in the blanket. Even though what comes through the door could be very dangerous, he has to get rid of the rumples first. Everything has to be tidy. That's even more important than the dangerous. If he doesn't make sure the bed is tidy and he turns his back then maybe it could get more untidy when he isn't watching. Or turn into some kind of monster. Or anything. So he can't turn his back until it's straight. It's that simple.

"Severus, my dear boy, how are you this fine morning?" Dumbledore's cheerful words seem to echo off the walls, his personality filling the room. Severus instinctively shuffles closer to Harry because Harry never does that, Harry never makes the world resonate with his presence, and it hurts to have the world filled with someone else, like he's being muffled and stifled underneath it all. And Dumbledore's robes are bright and garish and there is no symmetry. Nothing right. It's all wrong, all wrong.

Dumbledore doesn't seem to notice Severus's silent aches, for he just smiles in a grandfatherly fashion. "You're looking better. I daresay all you need is a little fresh air to bring some colour to your cheeks."

Severus shudders and shakes his head.

"Come, my boy, surely it's time for you to leave this room. Hogwarts is more than just one room, and we would very much like to see you outside of these walls."

"I can't," he mutters.

Dumbledore adopts a knowing expression. "Severus, I know it feels safe to stay within this room—"

Safe? Safe? Safe in this room where he can never know if the window will still be there when he wakes up or if the walls will change when he closes his eyes? Never knowing if what lies outside the door is just a Hogwarts corridor or instead a lava-filled cavern or an inferi-infested sea? There is no safety, there is no peace of mind. There is only the fear, fear, fear. But at least in this room he can straighten the rug and make his bed and count the stones in the wall. Outside is too big. He can't count the leaves on every tree. He can't count the blades of grass. And if he can't count them then how can he know if they're all in the right place or if they're moving and changing around him when he turns away?

"—but it is time to summon the courage to step outside. You may accompany Harry to his classes if that would make you feel better, but you must no longer remain in here, Severus. It isn't healthy for you."

Go to classes? With other children? All messy and untidy and never staying in the same place, never staying the same. Why should he go to classes? He finished school twenty years ago! He knows he doesn't remember everything, doesn't remember much, but he knows that. He knows that he should be twenty years older than he is, not practically Harry Potter's twin brother! And it was Dumbledore, it was all Dumbledore, and no one ever asked what he wanted, no one ever gave him a choice, they all just forced him to go along with their stupid plans and their stupid schemes and he's had enough! Enough!

He throws himself at Dumbledore, screaming in his rage, fists flying, biting and kicking and doing his best to hurt because he is hurting and why should this man, the reason he's like this, not hurt too? Then Harry is between them, gently pushing Severus away, holding his arms against his side so he can't claw and scratch, drawing him too far away to be able to kick, murmuring reassurances.

Dumbledore, Severus is pleased to see over Harry's shoulder, looks dishevelled and stunned. This is a good dishevelled because Dumbledore is Severus's blindspot, the one thing that can make all his strangenesses be forgotten. His rage overcomes the sickness in his mind, the sickness that is there because Dumbledore thought he knew best. Dumbledore thought the only way to hide Severus was to turn him into a sixteen-year-old boy and hide him in a school, and he didn't ask Severus if that was what he wanted, he just did it. And there's a reason witches and wizards get old just the same as Muggles do, and that's because anti-aging magic doesn't work. So now Severus is sixteen with holes in his memory and a sickness in his mind and he's stuck in this room counting stones and window panes while waiting for the castle to collapse in on him because it's only made of stone and stone isn't permanent and one day it will collapse and—

"Go away, please, Professor," Harry says.

"Harry, Severus needs—"

"He doesn't need anything you have to offer." Severus is gently pushed down onto his bed and he sits down unwillingly but also obediently because there is something in Harry's voice. He looks up at Harry who looks back even as he talks to Dumbledore. "You're doing to him just what you did to me. You're telling him what to do and what to think and where to live. But he doesn't have to do any it." He doesn't? Severus tries not to feel hope. "If he wants – if he wants—" Harry stresses, looking at Severus, "—I'll take him to the Muggle world. They have doctors who can help heal his mind."

Yes!

"Harry, there is really nothing wrong—"

"There is everything wrong with his mind!" Harry turns on Dumbledore with fury and Severus shrinks back. "You can't pretend there isn't, you can't pretend magic can fix everything! You can't pretend you didn't make another mistake! He's not your sister!"

The world freezes. Severus doesn't understand what that last comment means but he knows that Harry has scared Dumbledore. Wounded him in a way Severus could never have hoped to achieve.

"How did you..."

"Did you think Voldemort wouldn't try to learn all your dirty little secrets in his attempts to defeat you? And did you think this damn scar, this damn link, gave me nothing? Severus isn't broken, he's just sick. And he doesn't need to be hidden away and he doesn't need to be forced to be something he's not! I'm not going to let you treat him like a cross between a leper and a liar just because you're too scared to face all that again. He's Severus, not Ariana. And he's not your problem." Harry turns his back on Dumbledore, dismissing him. "Would you like to come, Severus? I'll give you a room, just like this one if you want. And you'll be okay there."

"They'll make me better?" He wants to be better. He wants to stop being afraid and stop counting things and stop being wrong all the time.

"They'll try. But even if they can't they'll understand."

Understand. People who understand. Like Harry. Not like wizards. Not like Dumbledore. "I would like that," he says.

Harry nods. "Okay, then. Dobby will take you to the new place, are you okay with that?"

"Not outside?" Severus checks. Outside is too big, too much.

"No. He'll take you straight to your new room. If you're happy to let him."

Severus thinks about it. Dobby is the one who brings his meals. Dobby makes sure that everything is proper and symmetrical. "That is acceptable."

"Harry—" Dumbledore looks shattered, as if Harry has somehow broken through to him. Severus may not remember everything but he remembers enough to know that Dumbledore has never looked like that before. Harry doesn't look at him and Dumbledore's eyes turn to Severus. "Severus, my dear boy... I'm—I never meant for it to be like this."

"That's the problem," Harry says tiredly. "You never do. You always try to do what's best but you never think. So we're going to fix our own problems. Because we can, if you just let us. You don't have to be the hero, you don't have to be the one in charge, you can just leave us alone to live our own lives. We're perfectly capable, you just never give us the chance."

"I just want to protect you all."

Harry meets his eyes. "I know. But you need to learn to let go."

"Harry—"

"No, you listen to me, Dumbledore." Harry straightens, back ramrod straight and stiff, looking Dumbledore in the eye. He's almost the same height as Dumbledore now, and Severus sees the startled realisation in Dumbledore's eyes. This is no longer the boy destined to destroy Voldemort, this is the young man who defeated Voldemort. Severus doesn't think Dumbledore ever realised that before now, not in the months since the Dark Lord's defeat. But he sees it now. Harry stares him down. "You listen to me," he says, quiet and sincere, and though his personality doesn't fill the room the way Dumbledore's does, it is unmistakeable. "Voldemort held onto his hate and destroyed himself. You hold on to what you love and destroy us. Let it go, just let it go. Let us go."

Dumbledore backs down – Dumbledore! who never backed down to anyone in his life! – and bows his head. "Very well, Harry. Whatever you choose, I will not interfere." He looks between the two of them, looking old but hopeful. "But please, both of you, if I may still perhaps visit—"

"I won't cut you out of my life," Harry says. "In your way, you love us, I know that. But you don't have to be responsible for us, you don't have to make the decisions for us."

Severus agrees, for the sake of the memory of the desperate need in Dumbledore's eyes when he turned Severus into this. But there is nothing in that that says he must like it, and so he makes no attempt to ease Dumbledore's conscience. Harry has always been more forgiving than he. Besides, agreeing makes the man leave. Severus is glad to see him go. Glad.

Harry turns to him as the door clicks shut and there is relief in his eyes, as if for all his bright words he is as glad to be rid of Dumbledore as Severus, he's just better at acting how the world thinks he should instead of how he wants. That makes Severus feel better.

Harry smiles. "So, I'm guessing you don't want me to pack for you?"

Severus winces at the thought of Harry packing, of the mess that would be in the suitcase, no neatness or careful creases or straight lines, but he recognises the joke as well and manages to smile back. "No." He's going away, somewhere where people will understand him and where there will be no Dumbledore. Severus's smile widens. "Thank you."