A/N:

written for a promptposted by Alex (immxrtalbi) on tumblr! thanks for letting me write this out!

original prompt:

Harry enters in the mirror of erised and everyone is the complete opposite of themselves. And when he meets Tom—who's supposed to be arrogant, rude, and cynical—he's actually sweet and kind and helpful in the mirror world, well, Harry falls a bit in love with him. Except his Tom, aka his asshole best friend, wants to take him back in the real world. Yeah, Harry is happy where he is, thank you very much. But knowing that he can never say no to his Tom, Harry leaves. It's a shame the mirror has a mind of its own.

onsider this to be my halloween fic for the spooky season. funnily enough, last year i also wrote a halloween fic that also centered around mirrors. second time's the charm?

my last bit of commentary is that this first chapter marks a total of over 1,200,000 words posted over two years of writing tomarry. very very crazy. thank you all for reading and supporting what i write.

.

Equivalent Exchange

.

Part One

.

If I said you're all I want and more

Fingertips and collarbones

If I caught you on your own

Would you mind my hand stitched into yours?

.

—Dream, Tessa Violet.

"Harry. Harry. Wake up."

Harry flailed and caught whoever it was in the shoulder before they clapped a hand over his mouth and closed his wrist up in a vice-like grip with their other hand.

In the darkness and without his glasses, Harry could not make out the face of his attacker, but as the blurry shape in front of him slowly focused, he thought he knew who it was.

Harry wrenched the hand off of his mouth. "Tom?" he hissed angrily. "What the hell?"

Tom lifted Harry's hand up and shoved his glasses into them. "Get up. I need you to come with me."

Harry put his glasses on and attempted to hit Tom in the shoulder a second time. Tom leapt backwards with ease, and so Harry lunged after him and managed a decent hit to the stomach before landing sprawled half over the edge of his bed.

"You're a git," Harry said in a harsh whisper, scrambling to sit up. "What are you even doing at this hour?"

"I found something. I want you to come see." Tom folded his arms over his chest, clearly impatient. "Hurry up. We'll need your cloak."

Harry snorted and stuffed his feet into his shoes, sans socks. This better not take long. "Prefect Riddle afraid of being caught out after hours, is that it?"

"You're going to wake half the castle with your racket," Tom said, which meant yes.

Harry slid off the bed and rummaged through his trunk for his cloak. It wouldn't cover them both completely, but no one would notice disembodied feet at this time of night.

"Let's go," Tom said, already heading for the door.

Harry hurried to follow and, once they reached the foot of the stairs that led into the common room, threw the cloak over them both. Now came the awkward part of walking like a four-legged unit until they reached wherever it was that Tom wanted them to go.

"If you step on my foot," Harry said quietly as they crept past the empty fireplace and towards the portrait hole, "I will leave you behind and go back to bed."

Tom shifted like he was adjusting himself, his elbow bumping sharply into Harry's side. "It isn't my fault you can't keep up. Try lengthening your strides."

Harry held his tongue at the jibe and resigned himself to silence as they walked down the corridor that led to the grand staircase. Slowly, they made their way through the castle. Harry thought they might have been headed towards the library. If Tom had woken him up to show him a book, Harry was definitely going to kill him.

"Where are we going?" Harry finally asked, when his curiosity could no longer be held at bay.

"We're nearly there," Tom muttered. "It's just this way."

They entered a dusty, disused classroom. Tom shrugged the cloak off and shut the door behind them. Then he retrieved his wand and cast multiple locking charms on the doorknob.

"That won't keep any teachers out," Tom said, "but it ought to stop anyone from accidentally wandering it."

"Still don't know why we're here," Harry said pointedly.

"There's a mirror." Tom seized Harry by the elbow and dragged him towards a sheet-covered structure in the back corner of the room. With a wave of Tom's wand, the sheet flew off, revealing a large, ornate mirror with a gold frame and clawed feet.

From this angle, Harry could see half of himself and Tom in the reflection. "You know," Harry said, "I always knew you only ever thought about yourself, but to see it confirmed like this is really something else."

"Shut up." Tom roughly steered him a few steps to the right. "Tell me what you see."

Harry looked at the mirror. "I see us," he said dully. "If I'm being more specific, I see myself standing next to an idiot that I'm not speaking to for the rest of the day."

"Really look," Tom insisted, seizing Harry by the head with both hands as if he could direct Harry's line of sight.

"Get your hands off me, you berk," Harry protested, swatting at Tom's arms. "I'll look, just stop it."

Tom dropped his arms and took a step back. He sounded vaguely breathless as he said, "Tell me what you see, Harry."

Harry stared at the mirror. His nose was itching from all the dust. The mirror showed him standing in his pyjamas and Tom standing behind him a meter or so away.

"I don't see anything," Harry said.

"Just... wait. Just wait a little longer. The magic might take some time to work."

"Alright." Harry stuffed his hands into his pockets. The reflection continued to display the same thing.

In the mirror, Tom crept forward, brows furrowed. His eyes were fixed on Harry. He reached out carefully and then, after another pause of hesitation, laid his hand on Harry's shoulder.

Harry lifted his own hand to his own shoulder. There was—there was nothing there. He whirled around, mouth agape, to see that his Tom hadn't actually moved at all. Tom raised a brow at him as if to say 'I told you so' and jerked his head toward their reflections.

Bewildered, Harry turned back to the mirror. The reflection of Tom still had his hand on Harry's shoulder and he was... he was smiling. His eyes were bright and he looked so happy. He looked happy to see Harry standing next to him.

"Tom?" Harry whispered. His feet carried him forward, forward, closer. He was inches from the glass, from the Tom in the mirror. Harry raised his hand again, confused but intrigued, and was startled when the Tom in the mirror mimicked his actions.

"Do you see?" said Tom from somewhere over Harry's shoulder.

"Yeah," Harry said. In the mirror, Tom's smile grew wider. He laid his hand against the glass, fingers spread, and glanced meaningfully at Harry's own hand.

Transfixed, Harry closed the remaining distance and pressed his palm against that of Tom's reflection. The glass was cold beneath his hand, like ice water. It felt strangely... not solid. Lightly molded to his hand.

"Harry?"

Startled, Harry went to turn around again but found his hand was stuck to the mirror. "I—" Harry began, his eyes sliding to the reflection once more.

Mirror Tom's hand was lined up perfectly with Harry's. He looked just as confused as Harry felt.

"Hold on," Harry said, trying to yank his hand back. It wouldn't budge. He met eyes with Tom's reflection self, panic slowly rising in his chest. "I'm stuck, Tom." Which Tom he was talking to, he wasn't sure.

The Tom in the mirror pulled back. That was to say, he stepped away from the glass, his hand departing with him, and Harry's entire body lurched forward in response, as if their hands had been glued together by a mysterious force.

Harry expected to smash face-first into the mirror and knock the entire thing over. He did not expect to sail straight through the glass, the veil of it washing over him like a heavy winter breeze, and fall directly into Tom's arms.

Tom let out a sharp cry of pain as he tumbled backwards, Harry collapsing awkwardly on top of him as they both landed on the hard stone floor.

"Sorry," Harry said on instinct, scrambling to roll off to the side so as to relieve poor Tom of his weight. "Sorry!"

Tom sat up with a low groan, rubbing at the back of his head. "That hurt."

"Sorry," Harry repeated with a wheeze. Then he glanced over at the mirror. Had that... What had happened? Had he gone through the mirror?

"Harry?" Tom suddenly came into view, blocking the mirror from sight. "Are you alright? Did I hurt you?" Tom's hand came up to cup his face, thumbs smoothing gently over Harry's flushed cheeks. "Maybe I should take you to the Hospital Wing."

"I'm fine," Harry said, distracted by the sensation of Tom's hands on his face. "Are you okay? I fell on top of you."

Tom frowned. "I'm alright." He laid his hand on Harry's shoulder again, only this time his touch was warm. "Are you sure you're fine?"

Harry was unused to Tom showing so much concern. It was odd. "I'm fine, really." He nudged Tom to the side so he could see behind him. "What happened with the mirror?"

"I think you must have fallen through somehow."

Harry got to his feet and moved back in front of the glass. He could see himself in it, and he could see... Tom. Not the Tom sitting on the floor to his left, but his Tom on the other side of the mirror.

Tom's face was contorted in horror. He was close to the glass but seemed reluctant to touch it. Harry raised a hand to the glass and pressed down. It felt very solid. The two of them made eye contact and Harry shook his head. How was he supposed to get back?

"Harry? What do you see?"

"I see..." You, Harry did not say. "I see Tom. My Tom." Reluctantly, Harry turned to address Tom's counterpart. "How do I get back across?"

"I'm not sure." Tom stuffed his hands into the pockets of his robes. "I've never seen or heard about magic like this before."

"Is this another world?" Harry asked aloud. He glanced back at his Tom, whose expression had firmed into a look of determination. He mouthed words that Harry could not quite make out. Was he going to find help? Tom didn't like asking for help. Perhaps he would try to figure out how to bring Harry back through the mirror on his own.

"I'm not sure," Tom repeated. "Is he saying something, this other Tom?"

"I can't tell," Harry admitted. In the mirror, Tom pointed firmly at the ground. Telling Harry to stay put.

"Maybe we should go wake up a teacher."

Harry frowned. "Tom's telling me to stay here."

"It doesn't really matter who gets you back across first, does it?" Tom said reasonably. "The point is that we should find someone who knows more about this mirror than we do."

"I don't know," Harry said hesitantly. His Tom shot a grim look in the direction of the mirror before picking Harry's cloak up from the floor. He pulled it on, vanishing from sight. "Maybe we should wait and see what he does."

"Did he say when he'd be back?"

Tom hadn't.

Harry didn't want to end up stuck here all night, or worse, for days while his Tom tried to figure out how to free Harry from the mirror. "Which teacher would we go to? Professor McGonagall?"

"No," Tom said. "She'd probably have me expelled for trying to help you. We should go see Professor Snape."

"Professor Snape," Harry repeated, trying to make sure that he'd heard right. "You think Snape wants to help me?"

"He's the Defense professor," Tom said with a nod. "He'll know what to do."

Harry pinched the bridge of his nose. "Listen, Tom, I'm not sure what your Harry is like, but in my world, Snape hates me."

Tom's mouth curled into a rueful smile. "I think you'll find that this world is full of surprises, Harry." He extended his hand, palm up. "Trust me. He'll help us."

Harry cast a guilty glance at the mirror. If he could get back through before Tom got himself into trouble, that would be best for everyone involved.

"Come on," said Tom, giving his hand a shake. "Asking for help is the right choice. We have no idea what we're dealing with and I don't want to risk you getting hurt because he tries something stupid."

"Yeah," Harry said, shoulders slumping. "Yeah, you're right. Okay. Let's go... Go see Snape." Hopefully it would be quick and painless.

Tom stretched his hand out again. After a pause, Harry took it. Tom's hand was gentle as it closed around Harry's. He led them out of the room and into the hall without further ado.

Harry felt exposed without the Invisibility Cloak to shield him. "What if we get caught?" he whispered.

This Tom's steps were slow, measured. His eyes were sharp as they scanned the corridor. "It'll be alright. The dungeons aren't too far from here." He squeezed down on Harry's hand. "If we hear someone coming, I'll distract them so you can get away."

But no one came, teacher or student. Harry and Tom made it to the dungeons without trouble and came to a halt in front of Snape's private quarters.

Tom nudged him lightly. "You should knock."

"Me?" Harry said, baffled.

"Yes, you. He likes you more than he likes me."

Harry was beginning to wonder if this wasn't all a dream. "If you say so." He looked at the door and swallowed. "Are you sure you can't knock?"

"I suppose I could," Tom said. "But you'll have to greet him when he comes to the door. I'm telling you, Harry, he won't like it if he sees me first."

"Sure," Harry said. "You knock." Anything had to be better than knowing he was the one to wake up the dungeon bat at this ungodly hour of the night.

Tom knocked on the door.

After several minutes, Harry heard the locks clicking and shifting. Tom took a step away, nodding at Harry to move forward. Harry did not want to move forward.

The door opened, revealing Snape. He peered around the edge at the both of them, then threw the door open the rest of the way.

Harry steeled himself for detention and said, "Hello, professor."

Snape was presumably dressed in pyjamas, though he must have seen fit to throw on a set of dark robes before answering the door. "Harry?" he asked, concern wrinkling his brow. "Is something the matter?"

Harry? Harry was at a loss for words. He turned to Tom, pleading with his eyes, and was relieved when Tom stepped in and cleared his throat.

"While I was doing my patrols, I came across an enchanted mirror in an unused classroom near the library. Harry came through it by mistake. We were hoping that you would be able to help him return to his world, sir."

Snape narrowed his eyes at Tom. "Patrols? At this hour?"

"I thought I heard a disturbance, sir."

Never in a thousand years did Harry think he would see Snape glaring at Tom like the Slytherin prefect was nothing but potion residue on the bottom of his shoe.

"Sir, Tom said you might be able to help me get home," Harry interjected loudly, and Tom shot him a grateful smile in response.

"I will have to examine this mirror," Snape said after a pause. "Show me."

The three of them made the return trip to the unused classroom. Snape was silent for most of the journey, which made Harry nervous. He did not know what to make of this strange Snape who was nice to Harry and rude to Tom.

"How did you encounter this mirror, Harry?" Snape asked.

"Oh," Harry rubbed at the back of his neck, unsure how to explain. "Well, Tom—my Tom—woke me up and told me to come see it. I'm not sure why, exactly. But I saw Tom—this Tom—in its reflection and fell through somehow."

"That does not surprise me." Snape glanced sideways at Tom, who had a polite expression plastered on his face. "Perhaps you should learn from your counterpart's mistakes, Mr. Riddle, and avoid any future late night excursions lest you also find yourself trapped in a mirror." He smiled coldly. "Though I daresay I would be the last to notice your absence."

Harry coughed awkwardly. "Right, well, it's just this way—"

They entered the classroom. Snape cast a number of spells on the room before any of them approached the mirror. Nothing happened, though the sudden flash of spell fire caused Harry's vision to spot oddly.

Snape frowned and stepped further into the room. "Tell me exactly what happened."

Harry recited everything that had happened from the moment he and Tom had entered the room to when he had fallen through the mirror.

Snape's frown lines deepened as he approached the mirror and cast more spells. The bright whites and blues faded into the golden frame, leaving no traces behind. "This is old magic," he said eventually. "It will require more research."

Harry's heart sank. "Maybe we should ask Professor Dumbledore?"

To Harry's left, Tom shook his head rapidly back and forth.

"We are not yet that desperate," Snape said grimly. He tapped his free hand idly on his chest in a thoughtful manner. "We have the rest of the holidays to find you a way home. The school remains mostly empty in the meantime. You may stay with... Mr. Riddle... I suppose, until I locate a solution to your problem."

"But what about my world?" Harry asked, thinking of Tom. His Tom. "People will notice I'm missing."

"You can write a message," Tom said kindly. "We can tape it to the mirror."

That did not seem adequate, but what else could he do? Harry nodded with reluctance. "I guess."

"I will find a solution," Snape repeated. "Don't worry, Harry."

It was hard not to worry when Snape was calling him 'Harry'.

Snape conjured a piece of parchment and, surprisingly, a Muggle pen. Harry scribbled down a note to let Tom know what had happened and attached it to the glass of the mirror with a Sticking Charm. He would come back in the morning to see if Tom had left a note of his own.

"I'll take Harry to the Slytherin Common Room," Tom said once it was done. "He can stay in my dorm."

Harry felt bad for leaving the mirror behind. Back in his world, Tom would be distressed and angry, furiously searching for answers. But there was little to be done so late in the night. When morning came, they would tackle the problem again.

"I'll expect you both at breakfast," Snape said sharply with a nod.

Harry supposed he should be glad he had ended up in a world where everything was relatively the same, even if Snape's behaviour was downright disturbing.

He and Tom left the empty classroom. As soon as they were out of Snape's sight, Tom reached for his hand again, lacing their fingers together.

"I don't have anything with me," Harry realized as they continued to walk. He looked down at himself. "And I'm wearing pyjamas." He didn't even have socks on, for god's sake.

"It's fine," Tom said reassuringly. "We'll get you everything you need."

Harry attempted a smile. "Thanks, Tom." He felt better with Tom around, if he was being honest. And this Tom was so nice.

"Professor Snape will figure out how to get you home," Tom added.

"I hope so."

They reached the entrance to the Slytherin Common Room. Tom said the password and held the door open for Harry to pass through. "I'm the only one here for the holidays," Tom said quietly. "So you don't have to worry about other people finding out about you."

That was a relief. Harry nodded. "Okay. And we'll be staying in your dorm?"

"I think it makes the most sense."

Harry couldn't argue that. Next, they descended a second set of stairs that led further under the lake. Then Tom led them to the sixth-year boys' dorm and held that door open for Harry as well.

The dorms, at least, were well lit compared to the eerie green tinge of the common room. Tom strode over to the beds and threw open one set of curtains, revealing the neatly-made emerald green bedspread within.

"You can have my bed," Tom said. "I'll take someone else's."

Harry felt his face grow warm. "You don't have to do that. I can just sleep anywhere, really. Maybe we can just put some of the blankets on the carpet?"

"Don't be ridiculous. You're a guest." Tom spun around and smiled. It was then that Harry realized that this Tom's eyes were not a rich brown, as he'd assumed they were. Rather, they were an unnatural shade of deep burgundy.

"Still," Harry said, "I'm not about to put you out of your own bed."

Tom had already peeled back the covers and was now patting the empty space. "The sooner you sleep, the sooner morning will come."

Harry shook his head. "You take the bed," he insisted. "I'll just kip on Malfoy's or something."

Tom released an impatient sigh and let the covers drop from his hands. He came to stand in front of Harry and with slow, careful movements so as not to startle, picked Harry's glasses off of his face. Harry was too shocked to move or protest; he merely watched as Tom gently folded the frames shut and set them on the bedside table.

"Get some rest," the blurry form of Tom murmured.

Something about the low tenor of his voice made Harry's heart quiver.

"Preferably without your shoes on," Tom added, and Harry hiccuped a laugh, half-hysterical, as the situation finally sank in.

He had stumbled into a world where Snape was nice and Tom was... sweet. Fear of being stuck here aside, Harry felt oddly at ease. Tom was his best friend, in any universe it seemed like, so he was not truly alone.

"Thanks for helping me," Harry said at last. "I think I'd be losing my mind if it wasn't for you."

"Of course. I will always be here for you, Harry." Tom set a heavy hand on Harry's shoulder. "Now sleep."

Tom's hand slid away, trailing down the line of Harry's arm. Without thinking, Harry snatched up Tom's hand with his own before Tom could pull away entirely.

"Wait," Harry said. In this unfamiliar room with only Tom to anchor him, he was suddenly reluctant to be alone. "We could share?" His voice wheezed in a pitched way at the end of his sentence, much to his embarrassment. "The bed," he added with a cough.

Tom blinked at him. Much to Harry's surprise, his cheeks had gone pink.

"I mean, Malfoy's pillowcase probably smells like hair products," Harry muttered. "I don't fancy suffocating to death in my sleep."

"Of course not," Tom said, too quickly. His small smile brightened up, and Harry found himself wishing that his Tom would smile more often. "Which half would you like?"

"Either works." Harry toed off his shoes so he would have a task to occupy himself with. Only once he was done with that, there was nothing left to do except stare at Tom. Or at the bed.

Tom made his way round to the other side to shut off the lamp there. Harry exhaled a sigh of relief and settled on the right side of the bed. The sheets and covers were cold. Soon, however, they would be warm.

Harry felt heat rise to his face again and was grateful for the darkness as the left half of the bed dipped with Tom's weight.

"Everything alright, Harry?"

Harry was still sitting upright. "No. Was just lost in my head. Sorry."

He laid down, careful to stay as far away from the center of the bed as possible. Then Tom pulled the covers over them both while Harry focused on keeping his own body as motionless as possible.

"Good night," Tom whispered.

"Good night," Harry said, trying not to think of how he could feel Tom's body heat radiating from the left side of the bed. He shut his eyes and attempted to relax.

Tom's breathing evened out long before Harry's did, faint snores that were hardly snores at all drifting into Harry's ears, but eventually Harry slipped into a deep, dream-free sleep.