SUNSIDE
"You know," said Twilight to Applejack as they trod along the path, leaving Ponyville behind them, "this would be so much easier if you let me lead."
Applejack snorted. "And give you the chance to escape?" she said, laughing. "Not a chance. I know the way. I think. I can lead fine," she added before stumbling over the cast on her leg, making the other ponies slow their pace again.
From the back of the line, Rainbow Dash rolled her eyes. "This isn't going to be like the time you tried to take us to Zecora's, is it?"
"We got out of that okay, didn't we?" asked Spike, who was riding on Rainbow Dash's back. As he spoke, he lost his grip on Rainbow's coat and nearly toppled, and he had to grab onto her mane to avoid from falling off altogether.
Rainbow winced from the pain, but said nothing as Spike climbed up her mane and back into position. "Eventually," she said. "After a certain dragon panicked and started sending random sticks over to Celestia. We're lucky she was smart enough to figure it out." Her voice then dropped an octave, and each words emerged from her lips separately and covered in malice. "She summoned the Royal Guard to find us. I've never been more humiliated in my life."
"Sure you have," interrupted Fluttershy, who was walking alongside Twilight in the middle. "What about Rarity's botched fashion show? Or that incident back at Flight School in the principal's office?"
"Which one?" asked Rainbow, who had visited the principal more times than she could count on her two front hooves. Which was to say, she had been more than twice.
"The only one where the principal hadn't called you there. Remember, you made me promise never to tell anypony about it?"
"No..." said Rainbow, still trying to narrow down the possibilities.
"I think it involved a certain griffin and a can of axle grease, among some other things," recalled Fluttershy.
"Right..." moaned Rainbow Dash. "She didn't even go to the same school, you know that? Some snooty private school."
Rarity, trotting next to Rainbow Dash, broke her silence. "This nostalgia is nice and all, but it doesn't exactly explain what is going on here."
Spike shrugged. "You've got me," he said. "I'm as lost as you are."
Pinkie Pie, who had managed to refrain from speaking by hopping in circles around the other six, found an opportunity to join the conversation and seized it. "Twilight's been acting all funny because she's not Twilight," she said.
"Yes, yes," muttered Rarity. "You explained that already. But where are we going?"
"Sky Mirror Lake," answered Twilight. "I can explain things better once we get there. Trust me."
"Not likely," huffed Applejack. "I'd trust ya about as far as I can buck ya. I wouldn't put it past ya to run away."
"I can teleport, O-" Twilight paused. "I mean, Applejack," she finished. "If I didn't want to cooperate, I'd already be halfway to Stalliongrad."
"Jus' don't talk," ordered Applejack. "The next time you open that muzzle of yours, it better be explaining what the hay's goin' on around here."
To Twilight's relief, Sky Mirror Lake existed sunside.
Sunside was the word she had used in her notes to describe this world, and it made sense. The side with the sun, even if it wasn't sunny all the time. Now, as the group neared the water's edge, six pairs of eyes turned to her, expectantly.
"Okay," she began, her voice shaking. "I want you all to imagine that the world is like this lake."
Applejack's eyes narrowed. "Excuse me," she said insincerely, "but what does this have to do with you tellin' us where the real Twilight is, or what you're doin' here lookin' like her." She felt a shove against her shoulder, and she turned to see Rainbow Dash giving a glare.
"Let her finish," said Rainbow Dash. "She'll get to it."
Twilight shrunk back a little, frightened by the animosity. Fluttershy gave a small nod of encouragement, and Twilight continued.
"I told you, I am Twilight, just," She paused, not sure how to say it. She eventually decided to just explain it the way it was. "I'm her from another world."
"Horseapples."
"Now, as I was saying, imagine this lake is the world. Look into the water, and tell me what you see."
The others obeyed and began scanning the water for whatever Twilight was talking about. Fluttershy, noticing a school of fish, became distracted, giggling as they darted about. Applejack begrudgingly complied but didn't say anything. Pinkie Pie, rather than watch anything actually in the water, began making faces, using the lake as a mirror. Rainbow Dash looked over at Pinkie Pie's reflection and began laughing, filled with a sort of giddiness that could only happen around Pinkie Pie, and had to happen around Pinkie Pie.
"What do you see?" asked Twilight.
Rainbow Dash turned her head forward and examined her own reflection. "Just some kelp," she answered, "and rocks. And one very awesome pony."
"Exactly," said Twilight. Rainbow Dash raised her head, confused about what she had done to get the question right. "Your reflections," clarified Twilight. "If the lake is the world, then it has two halves. The part above the surface, where you are, and the part below, where your reflection is."
"You're Twilight's reflection," guessed Spike.
"And she's mine. In a manner of speaking."
Spike looked back at the water. "I guess," he said. "But wait. The reflections are exactly the same as us. Wouldn't that make your world just like ours?"
Twilight smiled. "An excellent observation, Spike. Which brings us to point number two: magic." She lifted a rock off of the ground with telekinesis. "Now imagine this rock is a spell. Watch what happens when I 'cast' it." She tossed the rock into the water, where it sunk to the bottom, creating a number of concentric waves at the point of impact. Pinkie Pie watched her reflection as it was distorted by the waves passing over it.
Fluttershy leaped away from the water and hid in the grass, while Pinkie Pie continued making faces in the water. "It's like a fun house mirror!" she exclaimed.
"Right," said Twilight. "Magic has a measurable 'rippling' effect of sorts on the other side. It's the use of magic that makes the two worlds different."
"Nah," said Applejack. "Look. The waves are already gone. They don't last forever."
Twilight nodded, trying to stay calm. "Right, Applejack, but remember this is just a model. When it comes to magic, the ripples can last a lot longer before they settle out. The point is, sometime in the past there was very powerful magic. Powerful enough to cause a major divergence between worlds that still hasn't resolved itself. That's why I don't know the things she knows. I'm not her; my life is completely different. That's why I wanted to come here."
"How?" asked Rainbow Dash, who now didn't know what to feel about the impostor. "What's so bad about life over there, on the other side?"
Twilight looked at the ground. Some part of her had been trying to convince her that the dark and barren world was only in her imagination, and it had taken all of her courage not to give up and believe it. "I never met any of you guys, for starters," she said. "You know the Summer Sun celebration, two years ago? That was the last day the sun rose in Equestria."
"Black Snooty?" asked Pinkie Pie.
Twilight stared at the pink mare, not comprehending. "Sure," she said at last. "This creature, Nightmare Moon, came to Equestria and covered it in eternal night. I was supposed to stop her. I failed. All across Equestria ponies are starving, and it's all my fault. But that's not important. The important part here is the rock."
"What's so special about a rock?" asked Rarity.
"Not what it is," corrected Twilight. "Where it is. The rock is on the other side of the water now. In the model, that means it's gone through the barrier between worlds. So, the question we asked ourselves was, if magical potential can travel across worlds, then why can't energy, or matter? What if it was possible to send a pony through to the other side?"
"We?" asked Rainbow Dash.
"Zecora and me. She was my assistant."
"So that's what you did," said Applejack, trying to regain control of the situation. "You couldn't stand to look at the world you created, so you ran away."
Rarity shot Applejack a glare. "It wasn't her fault, Darling, it's was Nightmare Moon's."
"We couldn't run away. We couldn't figure it out," said Twilight. "Our first experiments were with light. We were able to build mirrors that would subject the photons to a magical field, force them to cross over. It was a way to see into your world, and it worked both ways. That was how we met the other Zecora. It must be a strange experience, meeting yourself. I don't know if I'll ever get to know it, though."
"But you did," said Rainbow Dash, staring at the impostor that resembled her friend. "You had to have met yourself. You kidnapped her."
"Let me finish," said Twilight. "After that, we started to become a bit more ambitious. We could send small items across, even though it took a lot of energy. We could even control where they landed, to a certain extent. And then I guess we got cocky. Full of ourselves, because we tried it on a pony."
"And?" asked Pinkie Pie.
Twilight closed her eyes, once again imagining the poor mare's singed flesh and flaming mane. "It was a failure," she explained. "A catastrophic failure. I don't know what went wrong. Maybe we didn't have enough power. But she didn't go through all the way."
"What happened?" asked Fluttershy, and the look on Twilight's face, grimacing and about to cry again, told Fluttershy she had struck a tender chord.
"We needed two burial sites," answered Twilight, slowly, trying desperately not to relive the memories. "One on each side."
"Oh," said Applejack quietly, her calm breaking.
"I'm so sorry, darling," counseled Rarity, not sure what else to do.
"We gave up after that," said Twilight. "It wasn't worth losing somepony else. We just wanted to ease the suffering, do what we could. We started building a magical greenhouse that could grow food, even without the sun. If we couldn't bring back the sun, we could at least try and solve the hunger problem. I like to think we saved a lot of lives with that." Twilight smiled, knowing that she had done some good, even if it was just reversing damage she had caused.
"Twilight," interrupted Applejack. "This still doesn't explain how you came over here. You said you never figured out how to transport a pony."
"We didn't," said Twilight. "And Zecora moved on. But I didn't stop thinking about this place. It was an endless temptation. A paradise, just out of reach. If we could only find a way across. But we couldn't, of course. The power required increased drastically with mass. We might be able to manage a filly, but I wouldn't stoop so low as to experiment on somepony that young. We just needed some way to reduce the mass of the transfer. And eventually we did. It was a theory, something untested. But it was a way to cross over purely using things we already knew how to do. It didn't require any matter to be transferred at all. After all, a body is just flesh. It's nothing special. It was the mind we needed to get across."
"You mean a brain-switching spell?" asked Pinkie Pie, who had decided to approach the story as a riddle. She'd seen a spell like that in Twilight's library, but had failed to convince her friend to use it to prank Rainbow Dash.
"A memory exchange," corrected Twilight. "Not even the whole brain. Memories are information; they have no mass. The only requirement was that the two parties had to be in close physical proximity to each other, even if they were on other sides. I knew where she lived; I followed her enough with a mirror to figure that out. So I wrote a letter, asking her to come to the castle of the Royal Pony Sisters in the Everfree Forest."
"I remember that," said Rainbow Dash. "We didn't see anypony there, and then Twilight just collapsed. She woke up all confused and embarrassed, so I took her home. But now that I think about it, right before it happened, I saw something. Like a shimmer in the air, only there was darkness behind it." She looked back at the lake. "It looked like ripples. That was you, wasn't it?"
"Girls," interrupted Rarity. "You're missing the important bit. This means that Twilight, our Twilight, is lost somewhere in a world ruled by that... that tyrant Nightmare Moon. Hopefully, if she has an ounce of salt in that new brainpan of hers, she'll be hiding out somewhere safe. We just need to get the other Twilight to switch them back."
"It won't be that easy," said Twilight quietly.
"And why the hay not?" asked Applejack.
"Like I said, we need to be in close proximity to each other. I wouldn't know where to find her."
"You could build another mirror," suggested Pinkie Pie.
"Actually," said Twilight, biting her lip, "there's another reason it may not work. You see, I didn't mean to come to this world unprepared. I wanted to spend a week or two following her, figuring out how she behaved, how to blend in, but my hand got forced a little early. I was attacked."
"Attacked?" echoed Pinkie Pie with a gasp. Twilight nodded. "By what?" asked Pinkie.
"I don't know," admitted Twilight. "Whatever it was, it wasn't pony. And it hurt me, pretty badly. Left a giant gash in my face." She traced down the side of her face with a hoof.
Rainbow Dash was about to interject and ask why they couldn't even see a scar, but the answer dawned on her. "You mean you put our friend in a wounded body?"
Twilight nodded. "The wound was bleeding pretty freely, but I managed to get away from it. But it looked like a hunter, and I figured it was only a matter of time until it found me again. If I wanted to cross over, I had to do it then. It's been a week since then. I don't even know if my old body is still alive. If it received prompt medical attention it might be okay, but it wouldn't since she would have woken up in the middle of the Everfree Forest."
Rarity couldn't believe what she was hearing. "You jackanape," she whispered.
Applejack looked at Rarity, shocked. "Rarity!" she cried. "That language ain't necessary."
"Don't you get it?" shouted Rarity. "Twilight may be dead, and it's all because this pony here was so much of a coward that she threw our Twilight under a metaphorical dragon's nest to save her own flank!"
"Hey, now, we'll get her back," said Fluttershy, but none of the other ponies heard her.
"Enough!" shouted Applejack. "Now I don't know 'bout the rest of y'all, but I don't plan on leaving a friend of mine out to dry." She approached Twilight, staring her down. "There's a killer after Twi' right now because it thinks she's you. But I ain't gonna let her die. Yer going to find a way to get Twilight back," she said. "I don't care how long it takes you. And if you can't do that, then yer going to find a way to get us over there to save her ourselves."
"But without a sufficient power source..." Twilight began to mumble.
"No buts. You will save her, y'hear?"
"Don't worry," said Fluttershy. "You'll find a way. You do live in a library now, so you have plenty of research material. I believe in you."
Twilight sighed, resigning herself to the impossible task before her.
"Actually," said Pinkie Pie, "I may be able to help too."
Everypony stared at her. "And how do you plan on doing that?" asked Rainbow Dash.
"Well, not me helping, exactly," said Pinkie. "But I know a stallion who might be able to help Twilight."
"Who?" asked Twilight anxiously.
"Exactly!" shouted Pinkie Pie. Then her voice quieted. "Wait, no. Not 'who', but close. You know, he's that brown stallion with the hour glass cutie mark. I call him Whooves."