Nature vs. nurture. How much of somepony’s personality is determined by their circumstances and how much is determined by their innermost being, their heart of hearts, whatever you call it. Are cutie marks something set in stone, only to be discovered, or are they something that can be changed with outside intervention?
Obviously we cannot conclusively prove this one way or another at this time, because no two ponies are completely identical. As both cloning and time travel are heavily restricted we must rely on less precise methods, involving statistical probability, but even so…
As they entered the library Starlight considered how she could best help search the library. Minuette knew this place well, especially if her discussions with Perfect about how little Canterlot had changed were any indication, while Starlight had been out of touch with such things for years. But there was another way she could help search the library. When Perfect finished explaining their pass-phrase, Starlight walked up to Emerald and tapped her shoulder.
“Hey, can you help me find something?”
“Sure, what are you looking for?” Emerald offered.
“A book on practical spellcraft of divination magic.”
Emerald stared in awe. “You can cast divination magic?”
Starlight nodded. “I’ve used the spell I’m looking for before, but it’s been a long time and I never memorized it. I should be able to use it again with just a quick refresher.”
Emerald nodded and walked over to an officelike structure sitting on a wall. She looked around them, and vaulted over the counter, landing in a heap out of sight.
“Ow!” There was a short scuffle and she stood up. “I’m fine. Now, let’s see.” She examined something under the counter. “Divination. Practice. Ah, here it is. 1020.” Emerald bent low, but then stopped. She turned and opened the door. “Heh, heh, heh.” She walked out, closing the door behind her and headed off down the rightmost aisle. “This way.”
Starlight followed her, and after a short walk Emerald pulled a book off the shelves and offered it to Starlight. “So, what are you planning? A spell to find a pony across any distance? A new way to spot changelings?”
Starlight shook her head as she found the spell she sought. “Nothing fancy at the moment, actually. I’m just going to scan the library for magic. I don’t have anything specific I’m looking for, I just thought I’d try.”
“Cool. Mind if I join you?”
“Not particularly.” Starlight cast the spell, and Perfect looked to her eyes as though she had begun to glow, but Starlight knew that was something only she could see. She looked around, but nothing else started glowing, so she headed further into the library. “Do you have any thoughts on where to start?”
“The back wall. That’s the best place to put a secret passageway.”
Starlight shrugged and took a left when they got to the back. After they had gotten about halfway to the other side Starlight saw a bookcase on their right begin to glow. She walked up to it. “This bookcase has a spell on it. That, or it contains a magical object.”
Emerald scanned the shelf. “There,” she said, stepping close and pointing at a pair of books. One was yellow with a stylistic sun at the top, while the other was blue with a stylistic moon. Both had clouds of the same color at the bottom, feeding together as if they were the same picture. “I bet if we pull those a secret passage will open up.”
Starlight decided it was as good a plan as any, so she pulled the books out. Instead of floating off the shelf they tipped forward, the bottom of each spine refusing to leave the shelf. Starlight and Perfect waited, but after a few moments nothing happened. They looked at each other. “Maybe it takes a specific pony's magic?” Emerald suggested.
Starlight released the magic scanning spell. Then she lit her horn again and rested it against the place where the shelf hit the ground, closing her eyes. Then she felt the shelf as though she were trying to manipulate it with her telekinesis, yet applied no force. “There’s no wall behind this shelf. I’m going to see if I can teleport across and open it from inside. Please be quiet, this is still a new spell for me.”
Starlight focused on everything she knew about teleportation and the other side of this obstacle. She chose a point equally far from both the ceiling and the floor, just in case the passage rose or fell quickly. She didn’t want to think of what might happen if she teleported inside of something. When she was ready she took a deep breath, and cast the spell.
She appeared in darkness, and the first thing to happen was she fell and skinned her left back knee on cold rough stone. But she was on the other side, and mostly unharmed.
After a moment to collect herself she noticed it wasn’t completely dark. A faint light was coming from below, kept out of sight by a spiral staircase. In this dim lighting she examined the back of the shelf. To one side she saw a lever. She pulled it and the shelf slowly slid away, revealing Emerald.
“We make a pretty good team Starlight,” Emerald said, holding a hoof out. Starlight tapped it.
“Yep. What can you tell from this?”
Emerald leaned down, inspecting the ground. Then she peered around the passage they could see from the entrance. “It’s not abandoned. Somepony is keeping this place taken care of, sweeping the cobwebs and such.” She frowned. “Or someling.”
“Let’s see what they were guarding,” Starlight said, leading the way down the stairs. Emerald closed the secret door after them and they both used their hornlights to keep the passage from falling back into darkness.
“So, this is a pretty elaborate secret room, right?” Emerald asked. Starlight just nodded. It put her escape tunnel in the village to shame, that was certain. “And we’ve determined that the changelings aren’t big fans of making things, they just use things as they find them?”
“That does seem to be our expert’s opinion.”
“And this chamber is centuries old, if the wear and tear I’m seeing is any indication. Finally, the books were emblazoned with the royal sister’s crests. All together this leads me to a theory.” Emerald paused for a moment before continuing. “This place is no more of changeling construction than the library above.”
“I assumed it was built at the same time as the library. A construction project of this caliber would be hard to conceal, and it’s obviously a secret.”
“Yes, that’s another point in favor of my theory. Now the question is whether whoever is using this is with the changelings or an infiltrator like us.”
At this point they had reached the bottom floor. The stairs ended at a short hallway with two torches on each wall. They let their own lights go out, no longer necessary. At the far end of the hall were an ornate pair of wooden doors, with gold trim. Emerald grinned. “See! This is the sort of thing I was looking forward to at the old castle. We cheated past the first puzzle, but we’re unicorns, not pegasi. Nothing wrong with playing to our strengths.”
Starlight walked up to the door on the left. “Together?”
Emerald nodded. “Together.” They each grabbed their respective handle in their magic and pulled. Nothing happened. “Push?” Starlight shrugged and they pushed, both doors opening together, revealing a large cavern. There were books on shelves around the edges of the room, several red and gold banners Starlight didn’t recognize, and several other decorations. All this was lit by a fireplace on the far side.
They both wandered around the room, examining it in wonder. There were so many books Starlight didn’t think they’d have time to even read all their titles. This place was surely home to lots of rare and interesting knowledge, but with every passing moment Starlight was growing less and less hopeful of finding anything pertinent.
She turned to suggest they turn back, but then she saw something under the table in the center of the room. She walked over and pulled it out. It appeared to be an old and battered child’s stuffed doll.
“What are you two doing here?” called an angry voice. Starlight turned and saw Twilight standing in the doorway, staring at them. She was standing tall and imperious, holding a scroll in her magic.
“Twilight?” Starlight gasped. “Just give us a moment and we can explain! We’re not really changelings!” Emerald nodded.
“You’re not?” Twilight asked, anger fading into suspicion. “Prove it.”
“Of course.” Starlight closed her eyes and concentrated on the race change spell. Carefully she dismissed the spell only over her and Emerald. When she opened her eyes Twilight was writing furiously in her scroll.
“Fascinating. Few unicorns can pull off a spell of that caliber. Were you involved in defeating Chrysalis?”
“Yes, and we’ve come to ask for your help saving Equestria the rest of the way.”
Twilight raised an eyebrow. “Really? How do you plan on doing that? I’m sure you’re a powerful mage, but I can personally attest it will take more than that to defeat the changelings.”
“We have a set of magic artifacts that should be capable of defeating the changelings, but they require the six bearers to work together to use them. We already have two, and you would be the third.”
“Should? How sure are you that these artifacts will work? More importantly, what can we do to assure a favorable outcome?”
“None of us have any firsthoof experience with them,” answered Emerald. “So we’re not quite sure how exactly they work. But we know they’ve defeated several ancient and terrible foes, so we believe they will work here as well.”
“What artifacts are we talking about?” Twilight asked.
“The Elements of Harmony,” answered Starlight and Emerald together.
Twilight teleported a book to her side and flipped through rapidly. Then she glanced between one of the pages and her scroll. “How do you know about the Elements? They have been lost to time, known only in passing even to scholars. The only surviving records speak of one bearer and one foe.”
Starlight sighed. “I know this can be hard to believe, but I have proof if you’ll bear with me.” Twilight nodded and readied her quill. “Our team comes from another reality. We’ve come here to help repel the changelings and windigoes. After that, we haven’t really made a plan. If you would like, I can open a portal to our home dimension.”
“First, could I see what you use to pass to this other world?” Starlight nodded and pulled out her beacon.
Twilight took it and scanned the crystal. “Incredible. Its enchantments are similar to the portal mirrors, but it’s evocation, not conjuration. How does it work?”
“We call our friend and ask him to open a portal on the nearest mirror,” Emerald explained.
“Thank you for helping me to understand,” Twilight said. Her horn flashed brightly and over a dozen changelings marched into the room. Twilight grinned smugly. “Surrender quietly and you won’t be harmed. I look forward to further discussions with you after the current crisis has been dealt with.”
“Why were you pretending to be a pony?” Emerald asked. “We looked like changelings!”
“Oh, I’m not pretending. We don’t let outsiders know this, but I’ve been working with the changelings ever since the invasion. Normally from the hive, but occasionally as a spy. It’s very nice to have a spy that can’t be revealed by divination.”
Starlight and Emerald stepped together back toward the fireplace. Twilight frowned. “I’d rather not have to use violence to bring you in, but I will if you won’t come quietly.” Starlight grabbed Emerald and cast a teleport spell to the library entrance, but nothing happened.
“You won’t be able to teleport out of this. I’m going to count to three, and then my guards and I will incapacitate you.” Emerald looked to Starlight. Starlight thought hard. Assuming this Twilight was about as powerful and talented as hers they would be evenly matched.
“One.”
She doubted Emerald could take on all the guards Twilight had brought, but some of them could have been with them.
“Two.”
Unfortunately they had no way of telling how many, or how many more might be outside.
“We surrender.”
“Good.” Twilight pointed at four of her guards. “Go bind their horns. No point in leaving unknowns in play.”
The guards stepped forward and put some sort of green slime on Starlight and Emerald’s horns. In mere moments it hardened.
“I know you’re new here, so I’ll give you a free hint. You can’t cast magic like that. Feel free to try, I won’t hold it against you. But don’t bother trying to overpower the guards.” She turned and headed for the stairs. “Follow me.”
Starlight and Emerald followed, guards taking positions before them and behind. It was a somber experience, and they could only hope the others would notice what had happened and find a way to rescue them. When they reached the top Starlight did a count and found a total of 19 changelings.
Twilight led them to the central area of the library, then she stopped and faced the group. “As I point to you, come forward and stand at attention.” She selected seven of the changelings and waited as they all trotted over to stand in front of her. Then she lit her horn and held the selected changelings in her telekinesis. After a brief moment they all flashed white and turned into the rest of the team. Pinkie, Driver, Fluttershy, Perfect, Sandstorm, Derpy, and Minuette, every single one held in place and revealed for all to see.
Perfect and Minuette fired beam spells at Twilight, who caught them in a shield. Half the changelings rushed forward and coated the unicorns’ horns and pegasi’s wings in the same slime they had used on Starlight and Emerald. Starlight just stared in mounting horror as their best escape plan went up in smoke.
Twilight hoofed one of the changelings Starlight’s beacon. “Take this to my chambers, I’ll need to study it further.” As the changeling flew off, Twilight grabbed Sandstorm in her magic and pulled her to her side. Then she conjured a knife and set it against Sandstorm’s throat. “I don’t need all of you alive, so I suggest nopony tries anything on our way to the dungeons. Do I make myself clear?”
Starlight hung her head. “Yes.” There was a chorus of similar answers from each of them except Sandstorm herself.
“Good.”