Princess Cadance wasn’t usually given to wandering around the palace in the middle of the night, but she also wasn’t used to an empty, cold bed, and it was far easier on her wounded soul to walk through the empty, silent corridors away from the public parts of the palace than try to sleep alone and remember everything she lost. She was only getting a few hours of slumber every day, but it came upon her instantly, and she was too tired and sleeping too poorly for nightmares to find her.

Something else found her, instead.

“Hm. Fifteen thousand SMUs,” muttered the pony. They were wearing a black cloak, which was somewhat unusual, but not quite as strange as the device they were manipulating with their hooves, clumsily. “That’s the strongest I’ve seen by a factor of almost a thousand! You’ll do nicely.”

Cadance blinked, looking around. There weren’t any guards in this part of the castle. Or at least, there weren’t any now. The castle staff was stretched a little thin, certainly, but somepony should have been here.

“Who are you?” She asked, cautiously.

“I’m not from around here,” the cloaked pony said. “But I have some complaints.”

She pushed back her hood, and Cadance’s eyes shot open, her exhaustion replaced by shock.

“Sunset?!” She asked.

“Oh good, that will make this part less awkward.” She reached into her cloak and produced a small canister, throwing it at Cadance’s hooves. The end burst open, and a cloud of gas that smelled a lot like chloroform surrounded her.

“What do you mean, foalnapped?” Twilight asked, frowning.

“Exactly what I said,” Princess Celestia said. “Princess Cadance is gone, and according to the guards -- many of them quite badly injured -- Sunset Shimmer was the culprit.”

“That’s impossible,” Twilight said, defensively. “She was with me. There are at least two other ponies that can back up our story, and I’m willing to submit to truth spells--”

“There’s no need for anything that extreme,” Celestia assured her. “I believe you. I didn’t call you and my former student here to accuse you of the crime.” She glanced at Sunset, who was sitting as far from Celestia as she could manage at the small table, wearing her armor even in the relative safety of the castle.

“What’s this about, then?” Sunset asked. “If Sombra has her, we need to get her back. We can probably hack together a tracking spell that can get through any kind of nondetection charm he might have on her.”

“I tried that already, but unfortunately I suspect Cadance is no longer in this world. Sunset already knows what I’m referring to.”

“...The magic mirror,” Sunset muttered.

“Indeed. It would explain why my own tracking spells failed, how the actual foalnapper was able to penetrate our defenses, and why she appeared to be a double of you, Sunset.”

“Perhaps somepony could explain?” Doctor Sparkle gave Sunset a significant look.

“I’m surprised she hasn’t told you already,” Celestia said. “Sunset Shimmer spent the last decade in another dimension. She decided she would rather flee this entire world than stay here and face the consequences of her actions.”

“Is that how you remember it? Because I remember it as escaping a prison sentence handed down by an insane tyrant who wanted to throw a kid in prison because she read some books she didn’t approve of.” Sunset folded her hooves.

“I suppose things can look that way when you don’t understand the big picture,” Celestia allowed. “Can we both agree that Cadance is more important than our disagreement?”

“Of course she is,” Doctor Sparkle muttered.

Celestia ignored her and looked pointedly at Sunset.

“Yes! Fine!” Sunset huffed. “You know I’ve been trying to be her friend, damnit.”

“You’ll need to go through the portal and retrieve her,” Celestia said.

“Wait, there’s something that stinks about this,” Sunset said. “The portal only opens once every thirty moons on this end. It shouldn’t be open now at all!”

“Ah, yes, under most circumstances you’d be right,” Celestia agreed. She stood. “Follow me.”

“We call it the embarkation room,” Celestia said. Sparkle walked past her to look at the array of humming devices surrounding the mirror, shoving a guard aside when he tried to stop her.

“You’re forcing the portal to stay open?” Sunset asked.

“Last year, when the war was at its worst, I decided to try looking elsewhere for solutions to my problems,” Celestia explained. “It was shortly after you decided to return to Equestria, but the mirror had already slammed its door shut when I wanted to see what the other side had to offer. Thankfully, I had Star Swirl’s original notes on the creation of the mirror portals.”

“Clever,” Sparkle said. “Who built this? I assume it wasn’t the idiot brothers, or it would have gotten somepony killed.”

“I did most of the work myself,” Celestia admitted. “This portal is a state secret. Only the EIS and my most trusted Magi are aware it exists. And of course, you and Sunset Shimmer.”

“Mm.” Sparkle nodded. “Wise. Did you get anything useful from the other side?”

“Yes, and no,” Celestia sighed. “Knowledge and information are easy to obtain, but we don’t have the manufacturing or materials needed to do anything with it. I have been using lessons learned from their history to improve our own strategy and tactics, but…”

Sunset raised an eyebrow. “What, guns are too complicated?”

“Methods to kill other ponies aren’t what we need,” Celestia said. “I’m trying to win the war with as few casualties as possible on both sides. I was hoping they would have less lethal options than bows and swords.”

“It’d be nice to get cell phones but I guess we’re a while away from managing that,” Sunset said.

“What’s important is that you’re familiar with the other world,” Celestia said. “Even my best agents have only a few weeks of exposure to their culture. You know it better than anypony. And…” she tilted her head.

“And I know how I think,” Sunset said. “So I’m the natural choice.”

“Indeed. I want you to find Cadance and bring her back, by any means necessary. If needed, I can provide you with any supplies or additional personnel you require, though I have been keeping our efforts there a secret from the natives, so I’d suggest you try and keep things from getting to the attention of the local authorities.”

“Yeah,” Sunset muttered. “Okay. And you can keep the portal open on this end indefinitely?”

“Even if it closes, we can get it back open relatively easily,” Celestia assures her. “It does get more difficult over time, but you will have days or weeks before there’s a real strain on this equipment.”

Sunset chuckled. “I remember when you refused to tell me anything about this bucking thing, and now you want to throw me through it. I always hated how much more you liked Cadance.”

“You also like her better than you like me,” Celestia said, not bothering to argue with Sunset.

“Yeah, and that’s the only reason I’m doing this. Sparkle, make sure she keeps the lights on.” Sunset waited for the Doctor to nod, then stepped up to the mirror, touching it with her hoof. The mirror surface rippled like water. Her brass wings fluttered at her sides, and she stepped through.

Sunset stumbled as her sense of balance fought to make sense of her body. Four legs, two legs, wings, it had been forced to deal with more changes to a body than the vast majority of people in her age group.

She caught herself and tried to look casual, glancing around to make sure no one had seen her step out of what was apparently the solid marble face of a statue. Thankfully, it seemed Sunset was alone for the moment. She brushed herself off, glancing down at her clothing.

“Guess it was too much to hope the armor would survive the trip,” she muttered. Instead, she had a white leather coat and pants, with neon green stitching.

“Sunset Shimmer?” Someone asked, sounding surprised.

Sunset turned. Vice-Principal Luna was looking at her in open shock. She seemed shorter, somehow.

“I don’t suppose you’ve seen me come through here lately, have you?” Sunset asked. “It would have been last night, probably. I think time is synced up right now.”

“Why aren’t you in class?” She demanded. “And are you wearing heels? You know they’re not in the-” She stormed up to Sunset and looked at her boots. “You’re not? Then why are you…?” She looked perplexed.

“Oh, guess I did hit a bit of a growth spurt,” Sunset shrugged. “Anyway, like I was saying, I’m looking for me. When’s the last time you saw me?”

“Yesterday?” Luna still looked perplexed.

“Awesome. Time probably is synched up. Do you know where I’m living, currently?”

“Are you having some kind of medical problem?” Luna’s brow furrowed. “Did you hit your head?”

“If that makes you feel better, sure.” Sunset put her hands on the older woman’s shoulders. “Now focus! Where do I live?!”

Cadance woke up slowly and, unfortunately, painfully. Her head was pounding, but she was okay with that because she was still alive, and sometimes you weren’t sure if that was going to be the case. She was also, at least for the moment, still able to think for herself, so she was two for two.

“Subject is starting to wake up. As noted, she assumed human form after exiting the portal. A cursory examination hasn’t revealed anything unusual in her physiology, but her blood tests are returning odd results. More detailed examinations will have to wait as I don’t have access to an MRI.”

Cadance opened her eyes and was immediately disoriented. She couldn’t see her muzzle! And her sense of smell and hearing were terrible! She was in some kind of basement or dungeon, tied to a chair and surrounded by strangely flickering and beeping devices that she didn’t have a hope of identifying.

“What--” she asked, her mouth feeling strange. “What happened?”

“Do not attempt to escape,” the thing in front of her said. It took a long few moments for Cadance to recognize her, and without hearing her voice, she might never have managed it.

“Sunset?” She asked, squinting at the strange figure.

The strange thing spoke into a small box, staring at Cadance. “The subject is able to recognize me even though I’m back in my normal human shape. Did she ever see my doppelganger while on this side of the dimensional fold? I’ll investigate further once there’s time. Establishing an exact timeline is a tertiary objective.”

“What’s going on?” Cadance asked. “Where am I?”

“I suppose I might as well explain things to you,” the strange version of Sunset said. She’d called herself… human? Was that what she was? “I need to borrow something from you.”

“I am not giving you my car keys,” Flash said. “Do you even have a driver’s license?”

“Not on me, no,” Sunset said. Poor Flash was backed into the lockers, Sunset cornering him, arm against the wall next to his head. “Look, this is an emergency.”

“Did you get taller? And…” He looked at her chest and blushed. She followed his gaze.

“...huh. Are they bigger? I hadn’t noticed.” She bounced a little. “It’s not important. Flattering, though. Flash, people are going to get hurt if you don’t help.”

“I don’t--”

“Starting with you,” she said. Her eyes flared with green light, and Flash yelped.

“What the hell was that?!”

“Hm?” Sunset raised an eyebrow.

“Y-your eyes!”

“Oh.” Sunset shrugged. “I’ve been busy… how long has it been?” She paused, thinking. “Maybe… a couple months? Yeah, that seems right.”

“I just saw you in school two days ago! And you-- you weren’t--”

“Yeah yeah yeah, I don’t have time to explain things to you, okay? Car keys!”

Flash fumbled in his pockets and produced a set of car keys. Sunset snatched them from his hand. Sunset took a few steps to leave and stopped, sighing.

“I’m sorry about this. I’d just ask for a drive but I really am worried about someone else and if you’re involved, you might get…”

“Hurt?” Sunset asked. She considered the device she was holding. “I’m not sure. I haven’t been able to test it. However, if I had to guess, I would assume that, yes, this will hurt.”

Before her captive could ask another question, Sunset activated the siphon. It had taken weeks - ages, for someone who could slap together a particle accelerator in her sleep. Literally. She’d gotten in a lot of trouble for that, especially since welding while sleepwalking was one of the fastest and most unusual ways to cause a major fire.

The siphon used technology that really shouldn’t work - it would be impossible to explain all the details to a layperson (and since no one else in the world was studying magic, as far as Sunset was aware, she was the only non-layperson.) If one could allow a metaphor, it was like trying to turn a circuit into an optical illusion that would fool the laws of physics long enough to do what she wanted.

Her captive - Sunset still hadn’t bothered learning her name, not that it mattered when she wasn’t even human - screamed, and pale blue energy emerged from her body like mist, flowing into the siphon Sunset had built.

The crystal array at the center started glowing.

“It’s working!”

“And where do you think you’re going?” Principal Celestia asked.

Sunset turned to look at her. She wasn’t nearly as intimidating as her pony counterpart. It was hard to be afraid of a mere school principal when you were regularly facing down somepony who looked and sounded like her but had the might of an entire nation (and a massive grudge) behind her.

“You know class isn’t dismissed until three, and according to Luna, you’ve been acting even more strangely than usual,” Celestia said. “I want an explanation, now.”

“I really don’t have time for this,” Sunset sighed, rolling her eyes and turning away. Celestia stopped her with a hand on her shoulder, holding her back, just a few feet from the front door.

Sunset spun, knocking her hand away.

“Don’t you dare touch me!” Sunset spat.

Cadance panted, sweat dripping down her face, the pain fading but still leaving a dull, empty feeling in her chest.

“W-why are you doing all this?” Cadance asked.

“Why?” Sunset sneered. “Do you even know what you aliens have done to my life? That duplicate you sent to take my place ruined my academic career! When I tried to transfer to Canterlot High, they already had my records! She stole my identity! She ruined my reputation!”

“Y-you can always explain it, and make new friends--”

“You think I care about friends?! She skipped weeks of classes! Because of her, they want me to repeat a year! ME!” She threw the wrench she was using across the room, and it hit the concrete wall of the basement hard enough to throw sparks.

“I’m going to use your magic to get my revenge.” She stormed over to the corner of the room, pulling the tarp off of a workbench and revealing a golden tiara. “It doesn’t look like much now,” she admitted. “But…”

She pulled on a thick rubber glove and carefully removed the glowing crystal from the siphon, gently securing it in a socket at the front of the tiara. Blue sparks traced along hair-thin gaps, revealing that the tiara was made of several interlocking panels.

“This will do just nicely,” she said, before putting it on. “What do you think? It’s a good look for someone about to prove that magic exists, make a few million dollars, and then stop your invasion!”

“W-we aren’t… invasion?”

“I’ve kept the portal under surveillance for several months. Agents from your world have been infiltrating at regular intervals.” Sunset tapped her new crown. “Now let’s see, I just need to…”

The crystal at the center started glowing, and the wrench she’d thrown floated upwards in a sky-blue aura.

“Hah! Perfect! Imagine what I’ll be able to do once I’ve had a chance to practice!”

Principal Celestia rubbed her sore wrist, looking at Sunset with concern. There was something very wrong with her student, and it wasn’t just that she was surrounded by swirling winds and green sparks, like a lightning storm in miniature.

“At least give me an explanation,” Celestia said. “You owe me that.”

“I don’t owe you…” Sunset started, then her expression softened. “You know what, maybe you’re right. You’ve always been a good principal. I shouldn’t blame you.” She offered Celestia a hand up, the dangerous aura around her fading. “Sorry.”

Principal Celestia accepted her help.

“A few months ago, at the start of the new school year, you weren’t acting like yourself,” Celestia said. “It was like you’d forgotten everything about your time here. I take it this is related?”

“Yeah…” Sunset rubbed her nose, thinking. “I don’t know how much you’d believe if I tried to explain.”

“Try me.”

Sunset shrugged. “You met the human Sunset, I think. I’m not from around here. I mean, I am Sunset Shimmer, and I’ve been attending classes until like a year ago, but I’m originally from pretty far away.”

“And if you aren’t human, then you’re, what, the last daughter of krypton? A shapeshifting bug from mars?” Celestia raised a skeptical eyebrow.

“I’m sort of…” Sunset coughed. “I’m a unicorn.”

“A unicorn?”

“About this tall…” Sunset sighed and put her hand at the right, very short height. “Yeah yeah, go ahead and laugh. It only sounds stupid because this world has weird connotations about unicorns! I’m one of the most powerful spellcasters in the world!”

“The most powerful human alive,” Sunset muttered, feeling the power flow through her body. Her body felt weightless, like gravity was only a suggestion. She flexed her fingers, sparks crackling between her palms harmlessly. She hadn’t had much time to actually research what magic could do, but direct experimentation was already proving to be-

A horn blared. She’d stepped out into the street to cross without looking both ways. Instinctively she threw her hand out to protect herself, as if she could stop the truck.

There was an explosion as a bolt of blue light tore through the pickup, ripping it and its driver to shreds, the shrapnel breaking windows on both sides of the street.

Sunset was totally unharmed. Fire alarms blared, and she started laughing.

“Did you feel that?” Sunset asked.

“Feel what?” Celestia questioned, distracted by the need to keep her car on the road. Driving Sunset where she needed to go would at least answer a few questions one way or the other, and she wasn’t about to give her student her car keys.

“There was a huge magical surge, right over-”

The sound of the explosion rumbled in the air, and a plume of smoke rose into the sky.

“You know what, you can probably figure it out,” Sunset muttered.

Sunset clutched the tiara around her head, the metal burning and humming.

“Come on!” She screamed, forcing it to still, getting her control back. “This is… harder than I thought it would be.”

The street around her would agree. Fires were already starting in a half-dozen buildings, cars were flipped over and thrown around like toys, there wasn’t an unbroken window in sight, and sirens were closing in from all directions.

Sunset took a deep breath. It smelled like smoke and blood.

“Okay, not the best way to start things off, but definitely impressive!” She smiled. “I just have to learn to control it.”

“Aren’t you a little short to be a natural disaster?”

The voice was familiar. She heard it all the time, when she was having an intelligent conversation. Sunset spun to see herself standing at the opposite end of the block, smirking at her like she was the subject of some private joke.

“You,” Sunset hissed.

“Gotta say, this isn’t what I’d be doing in your position,” her doppelganger said, indicating the destruction with one hand, her eyes never leaving Sunset’s. “Where’s Cadance?”

“Your disgustingly pink friend?” Sunset asked. “She’s alive, for now.”

“Give her to me and I’ll leave,” her double offered. “I’ll be honest, I don’t really care about this world. I’ve got bigger fish to fry. You give me Cadance, and I’ll just walk away. If not…”

“After what you did to me, I’d rather do things the hard way,” Sunset growled. She gestured to a flipped coupe and flung it at her mirror image. It smashed through where she was standing and into the building beyond, embedded halfway through the concrete, the car’s alarm blaring and distorted by the damage.

Her double stood on top of the car, having avoided it entirely.

“Sorry, kid, you’ll have to be a lot faster than that.”

Principal Celestia pulled out her phone, turning on the camera and hitting record.

The Sunset with the crown was getting more frustrated, tearing a streetlamp from the sidewalk with some kind of telekinetic force and throwing it like a spear at the Sunset in white, the slightly older Sunset dodging with superhuman speed, making it look casual and easy, frustrating her double even more.

“Sunset, you need to stop before people get hurt!” Celestia yelled. Both of them looked at her.

“And now you’re getting her involved?!” The crowned Sunset growled, the tiara sparking, moats of light trailing from it as she moved.

“For the record, that’s what it looks like just before a mega-capacitive storage crystal fails,” the taller Sunset said. “It’s why we don’t try to contain that many thaums in a single enchanted object, but someone who didn’t really understand magic might make the mistake. Even a lab-grown crystal isn’t good enough, no matter what the equations say.”

“Shut up!” The other Sunset yelled.

“Yeah, I have problems when I meet someone smarter than me, too,” Sunset said, circling her double.

“You aren’t smarter than me!”

“I’m not the one with an unstable magic capacitor strapped to their head, so excuse me if I have some difficulty believing you thought your brilliant plan all the way through. What’s the next step after you finish destroying downtown Canterlot? Gonna try and explain to the police that it was just a minor magical accident? I bet they’d love to hear that excuse.”

“Shut up!” The smaller Sunset roared, and her skin flushed red, then stayed there, darkening as the storm of uncontrolled magic around her flared up brighter.

Sunset gasped, the pain getting worse. She fell to her knees. Everything was going wrong. She felt her skin tear as wings erupted from her back.

“You need to get out of here,” Sunset said, suddenly next to Celestia. “This is bad.”

“What’s happening to her?” Celestia asked, as the smaller, or formerly smaller, Sunset screamed, her teeth visibly lengthening into fangs. She slammed a fist into the sidewalk, and the concrete cracked.

“I’m an expert in magical conditions and feedback, and I can assure you that, uh…” Sunset frowned. “She’s turning into a monster, I guess.”

“You guess?”

“It’s not like I’ve had to deal with some crazy human version of me trying to overdose on alicorn magic! This is a new one on me, too. I’m not even a hundred percent sure on the laws of thaumaturgical physics in this dimension.”

“So much for expertise.”

“Sure, complain at the person trying to save your life,” Sunset muttered. “That’s just like you.”

“Sunset, promise me you won’t hurt her,” Celestia said. “I can’t really stop you, but…”

Sunset sighed. “I won’t kill her. Good enough?”

“I just don’t want you to do anything you’d regret.”

Sunset started laughing. She was all-powerful! Sure, it had hurt at first, but now all she could feel was the magic surging through her body. Everything looked so small, now. Small and fragile. Especially her double.

“How do you like me now?” Sunset asked, grinning.

“I’m just not all that impressed,” her doppelganger shrugged. It was infuriating. How dare she act like she mattered? She was just a pathetic double, a wannabe!

Sunset flung a fireball at her, not even having to think about how to do it - she was so powerful now that the laws of physics were mere suggestions.

Her duplicate swept it aside with one hand, the flames disappearing, fizzling out with acid-green sparks.

“You’re like a foal having a tantrum,” she said. “I’d make some kinda joke about giving you a spanking, but you have this whole succubus thing going and I’m worried you’d take it the wrong way. I like myself, but not in that way.”

Sunset yelled and threw another ball of fire.

Princess Celestia wrinkled her nose in concern. An aurora of green and blue lightning surrounded the mirror, the once-calm surface roiling like a storm.

“This is getting too dangerous,” Celestia said. “Whatever is happening, it’s destabilizing the link between our worlds.”

Celestia’s horn flashed with light as she threw the emergency switches, shutting down the array holding the portal open.

“What are you doing?!” Sparkle demanded. “Sunset and Cadance are still on the other side! We can’t shut it down until they return!”

“If we don’t close the portal now, they might never return at all,” Celestia said, more sharply than she intended. “Star Swirl isn’t here to make more mirrors. We can’t risk damaging this one in whatever disaster is taking place over there.”

“You’re stranding them on purpose!” Sparkle growled and ran to the switches, trying to throw them manually. An aura of golden light surrounded her, casually dragging her away before she could act.

“We don’t know what’s happening,” Celestia reminded her. “That entire world might be ending! That’s the kind of power you’ve been playing around with. If something is destroying their reality it’s my duty to keep it from ruining ours as well. Can’t you at least understand that?”

“What I understand is that it’s very convenient that a copy of Sunset Shimmer managed to get through this heavily guarded portal without anypony noticing, kidnap an alicorn without a single guard raising an alarm, and escape with nopony challenging them,” Sparkle said. “It’s so convenient that it feels a lot more like it was planned by somepony else. Somepony who might not mind stranding Cadance in another world as long as it would get rid of Sunset for a few years.”

“Is that really how little you think of me?” Celestia looked offended. “Cadance is like a daughter to me!”

“So was Sunset, by all accounts, and that turned out rather poorly.”

“I’ll make every effort to save them, when it doesn’t put Equestria at risk.”

“And when will that be?”

Celestia didn’t answer.

Sunset stood at the edge of a parking garage, looking down at where her human (or formerly human, depending on how one counted a demonic transformation) double was flying, trying to figure out where she’d gotten to.

Having made a promise not to kill her was going to make things difficult. Not having a proper horn made forming more than the most basic spells nearly impossible. Pegasus magic worked fine, at least. She felt like gravity was only a mild suggestion - she’d been able to run right up the side of the building.

“If I’d been able to do this last time I was here…” Sunset mused. “I wonder if I would have bothered with school or gone right to trying to conquer the world?”

She looked down at her evil twin.

“I guess empirical evidence suggests I’d go mad with power.”

“THERE YOU ARE!”

Whoops. She’d gotten distracted. Sunset dodged to the side, the world slowing down as a blast of blue fire tore the facade of the building she’d been standing on to rubble.

The crown on her double’s head glinted in the flaring light of the barely-formed spell.

“Right, attack the weak point. Duh.”

Sunset tried to follow her duplicate’s movements, firing another blast of heat and missing by a country mile - she was moving too erratically for her to lead the attack.

And then her doppelganger was gone again.

“STOP RUNNING!” Sunset screamed, frustrated - and with how strong she was, her anger had a very real effect on the world. The asphalt under where she flew started to heat up, bubbling as the tar turned back to liquid.

A bolt of lightning struck her, not a full-size thunderbolt, really little more than a spark.

She looked up.

Her double’s foot slammed into her crown, the heel blazing with electric light. The crystal shattered under the impact.

Everything went white.

Sunset landed lightly, almost managing to negate the force of impact with pegasus magic. If they were good at anything, it was crashing into things and walking away.

Rain poured down, the wild clouds above reacting to the magic she’d unleashed and starting a torrential downpour. The fires across the few blocks of downtown started to go out.

Sunset ignored the storm and looked down to where the other Sunset had fallen, the human lying face-down in the street, her clothes torn to shreds.

“Hope I didn’t kill her,” Sunset muttered. She walked over and rolled her over with her foot.

Her double coughed and started coughing, curling up on herself and shivering in the weather.

“Should have known no version of me would die from a little magical feedback,” Sunset said. “Too bad you were born on this side of the portal. You would have been a pretty decent spellcaster. I should know.”

“Is she…?” Principal Celestia asked.

Sunset turned to look at the woman.

“She’s fine, but I’m pretty sure I told you to get out of here.”

“I wasn’t just going to leave. If something happened…” She trailed off.

“Were you making sure I didn’t kill her, or that she didn’t kill me?”

“I wouldn’t want either to happen.”

Cadance looked up at the sound of the basement door splintering.

Sunset ran down the stairs. Not the crazed one that had locked her up, the crazed one that had come to rescue her, and was slightly taller and with a bigger bust. Cadance noticed the bust right away. It was probably an alicorn of love thing.

“Sunset!” She gasped. “How did you find me?”

“I asked around for my own address,” Sunset said. She started untying Cadance’s bonds. “Had to make a pit stop and beat myself up a little.”

“Did you really spend years here?” Cadance asked, rubbing her wrists once they were free. “This place seems…”

“Awful?” Sunset asked. “It’s not great. No magic, the weather is terrible, and you have to get used to eating meat because let me tell you, these bodies really crave it. Fingers are nice, though.” She finished freeing Cadance and helped her up.

“Oof--” Cadance stumbled as she took a step, not used to being bipedal. “I’m glad I don’t have to get used to this.”

“Come on, Celestia is going to drive us back to the portal.”

“Princess Celestia is here?!”

“Not exactly.”

Principal Celestia raised her eyebrows as Cadance was helped into the back seat of her car.

“That’s the dean of Crystal Prep,” Principal Celestia said.

“H-hello,” Cadance said. “I’m Mi Amore Cadanza, but you can just call me--”

“Let me guess,” Celestia sighed. “Another double from horseland.”

“Oh. I guess Sunset filled you in.”

Sunset slid into the front seat.

“It’s funny, but I like this Celestia a lot more than the one I grew up with,” she said. “I’d try and come up with some clever plan to swap them, but it’ll have to wait until after the war.”

“War?” Principal Celestia frowned.

“Oh, didn’t I tell you?” Sunset said. “We’re at war back home.”

“No, you didn’t tell me.” Celestia tapped her fingers on the wheel, thinking.

“Let’s just get everyone and everypony back where they belong.”

Sunset put her hand on the statue. “Son of a MULE!” Sunset growled, kicking the marble. “Why is it closed?!”

“This is the portal?” Cadance asked. She ran a hand over it. “I can just barely feel the magic…”

“It’s supposed to be the portal,” Sunset said. “And it’s supposed to be open! Celestia was supposed to…” Her expression twisted into a sneer. “That clever bitch.”

Principal Celestia coughed.

“Not you,” Sunset sighed. She gave the woman an apologetic smile. “The other Celestia.”

“You shouldn’t use language like that. And…” Celestia hesitated. “Maybe it’s for the best. If the other world is at war, staying here would be safer. You could get hurt, even killed. If there are problems because of your… origin, I’m sure Luna and I can work something out.”

“That’s very kind of you,” Cadance said. She didn’t need to say ‘thanks but no thanks’ - her tone and sad smile did that for her.

“We need to get back,” Sunset said. “I have to make sure Doc Sparkle lives long enough to keep her promises, and Cadance is helping run the country.”

“Only when Princess Celestia is away. She doesn’t really let me do anything myself when she’s around.”

“Luna would probably agree that micromanaging is one of my worst habits,” Principal Celestia sighed.

“Luna?” Cadance tilted her head.

“Her sister,” Sunset explained.

“But she doesn’t have a sister in Equestria…”

Sunset snorted. “Anyway, I don’t think we have much of a choice. Unless we can figure out some way to pop this sucker open from this side, I’m going to have to go back to studying AP Bio, and you’re going to need to get a job.”

Principal Celestia’s trunk started making noise. It sounded a lot like a girl trying to escape by kicking near the latch.

“Oh right,” Sunset said. “I forgot about her.”

“You put her in my trunk?” Celestia groaned.

“I needed to make sure she didn’t run away!”

Celestia pressed a button on her keys, and the trunk popped open, the human Sunset gasping for air as she awkwardly scrambled out of the tight, dark space.

“You almost killed me!”

“No one has ever died from being locked in a trunk,” the taller Sunset said.

“Yes, they have!” human Sunset growled.

“No one important has ever died that way,” Sunset corrected.

“I guess that means you don’t want my help, then.”

“How could you possibly help?”

Her double crossed her arms. “I can get the portal open.”

“Prove it.”

“But I want something from you.” A cold breeze blew down the street. “Two things. First, something to wear so I’m not standing around naked in the middle of the street.”

“So you’re probably wondering why you were all called to this emergency assembly,” Sunset said, looking down at the assembled student body. “First, I just want to say that I’ve been blackmailing and bullying most of you for a couple years. Before you start looking at each other and wondering what dirt I have on the people sitting next to you, I’m not planning on releasing any of it.”

There was a collective sigh of relief.

“It isn’t because I’m turning over a new leaf,” Sunset assured them. “It’s because I don’t care. I haven’t even been here for months.”

The sigh of relief turned to confusion.

“You, get out here.”

She waved, and her double came out on stage. She was wearing some borrowed gym clothing and looking unhappy.

“This is the Sunset Shimmer that’s been here since I left, and you’ve been treating her like crap. She didn’t do anything to you. I just wanted you all to know that she isn’t me, you’re all buttholes for treating her like me, and I’m gonna check up on her in a couple weeks and if you aren’t treating her better, I’m gonna put everything I have online and you’ll all get to know each other’s secrets.”

She looked over the crowd.

“As a preview, here are some hints. Bedwetting. Janitor’s closet during lunch. Two people in the boy’s locker room before school. A certain teacher and what someone did for a better grade. I’m gonna guess based on the expressions I see out there that I’m understood.”

She dropped the microphone and walked off stage.

“Are you sure this is going to work?” Sunset asked. Her human double was taping electrodes and probes into place on the stone surface of Canterlot High’s statue.

“Look, the portal opens up on its own as it aligns. It isn’t a matter of needing to recharge or cool down, it’s more like a combination lock that cycles through all the combinations.” The other Sunset tapped a few times on the keyboard of a laptop hooked up to the mess. “What I’m doing it forcing it to the open alignment and holding it there. It wouldn’t surprise me if there was a device or spell specifically for this somewhere on your side.”

“Celestia had her own method,” Sunset said. “She didn’t make the original portal, though. It was Star Swirl the Bearded.”

“You had one of him, too? I should have known.” She huffed. “Of course it would be someone like him. He was either a genius or madman or both.”

“He was considered the greatest sorcerer of all time in Equestria.” Sunset smirked. “Of course that’s only because-”

“Are you really going to brag about this now?” Her double shot her a look. “I’m you. I know what our egos are like. Yes, you’re smart, How wonderful. I’m still the one who figured this out, so that makes me-”

“Better at technology and worse at magic.”

“You spent years here. Give me a decade in horseland and I’d be just as good.”

“No arguing,” Principal Celestia sighed. “Please.”

“Now, I don’t know for sure how stable this is going to be,” the human Sunset said. “There’s a lot of interference from the other end.”

“When you say stable, do you mean it won’t last long, or it might be a rough ride, or that it might kill us?” Cadance asked.

Sunset stopped typing and considered. “Yeah. All of those.”

There was a smell like ozone, and the portal cracked open, visible as a distortion like a heat haze in the very marble of the statue itself.

“I’m not sure about this,” Cadance said.

“Don’t worry!” Sunset took her hand, grinning. “You’re immortal, right?”

“Sunset!”

The world was spinning around her. It took a long moment for things to make sense, for her own two feet to realign themselves in her mind as her own four hooves.

Doctor Sparkle was being dragged out of the room by two guards in gold armor. They turned to look at Sunset, and from the fear in their eyes they realized precisely how much danger they were in.

She lunged forward on instinct.

A golden wall of magic rose up in her path.

Sunset’s cyan magic flared as her horn hit it, trying to push through. For a moment, the wall held, green sparks flying where the two met.

Sunset pushed harder, and her magic flared, color shifting to deep red. The wall shattered, and from the other side of the room Celestia cried out in surprise.

The two guards were thrown against the wall. A dozen more around the room leveled their spears.

“Halt!”

Sunset turned. Cadance had come through after her, though she hadn’t handled the transition as well, looking sick, sweating and pale.

“Let her go,” Cadance said. “Sunset Shimmer saved my life.”

“Ma’am, with all due respect, Princess Celestia--”

“It’s fine,” Celestia snapped. She took a deep breath. “It’s good to see you, Cadance. I was worried we’d lost you. When you’ve had a chance to rest and recover, I’d like to hear what happened.”

She walked out, her expression, for those who could read through her, as sour as if she’d been sucking on a lemon.

In a small lab packed with equipment in a windowless room at Crystal Prep, the guiding laser of a unique and hand-calibrated machine made quick passes over the remains of a shattered gemstone, the golden remains of the tiara it had been set into lying under a microscope.

“Interesting,” Twilight Sparkle said, adjusting her glasses.

A spark of blue magic pulsed from the broken gem.

“Very interesting.”

"Explain it to me again," Sunburst sighed. "You keep skipping over parts."

"I thought you read the abstract. I put it in your mailbox." Twilight Sparkle, grad student and still years from being a doctor, shoveled food into her mouth at the same time she spoke. It was unforgivably rude, but she'd caught the Princess's eye and nopony was going to correct her poor table manners.

"I looked over it," Sunburst said. He didn't want to say he hadn't understood a great deal of the paper.

"Okay, okay," Twilight sighed. "So you wear glasses. You know how a lens works."

"It bends light."

"Mm. Exactly. Optics are a complicated subject. There's a lot to do with the refractive index of materials. Convex and concave shapes. Focal points. That sort of thing."

"What does that have to do with magic, though? I could see how you were trying to combine the two but magic doesn't go through a lens like that."

"That's the point. My paper was about building a lens that magic can be focused through. The problem is that it requires an extra spacial dimension. If you think of a lens as a two-dimensional shape distorted through the third, this would require a three-dimensional shape that can be distorted through the fourth."

"So all you need are materials that don't exist, in an impossible shape."

"If you'd read the abstract you'd know I've outlined a few materials that would work. Really any of the magical materials, but Orichalcum would be best. Lunar titanium would be a close second--"

Sunburst was staring at her with such a flat look that it actually got Twilight to go quiet on her own.

Twilight frowned. "What?"

"Do those even really exist?"

Sparkle scoffed and reached into her saddlebags, throwing a misshapen scrap of metal onto the table between them. it was twisted and bent but had clearly been part of something larger. The metal was as dull as lead but had a blue shimmer to it like worked silver.

"Where did you get that?" Sunburst asked.

"An archaeology student. She owed my mother a favor."

"It can't really be..."

"Read the abstract," Twilight said, putting her hoof on the coin-sized scrap when Sunburst tried to take it. "And then we'll talk."