They had gone to sleep, Twilight and Sunburst on the bed, Moon Dancer given a fluffy makeshift bed on the floor.
When they awoke, she was not there. She was curled up on the bed towards its base, their hooves just shy of touching her. Sunburst was the first to awaken and discover this, blinking softly in the gloomy room. He was confused at first just being in a strange room on awakening, but there was Twilight.
She was a calming presence, a smile on his face before he sat up and his back hooves brushed against something warm and soft. "Huh?" He magicked over his glasses onto his face, squinting at the lump that slowly resolved into being a sleeping Moon Dancer.
She rolled over in place, her eyes open. "I hope I didn't startle you."
"Oh, um, no... but why are you on the bed... with us?" He moved to slide to the floor with a soft clop. "There was barely any room."
"It was better..." She sat up, eyes on him, though glancing towards Twilight. "May I be honest?"
"Please."
"I am incredibly jealous... Not in the 'ha ha ha, let's plan some stupid revenge' kind of jealous. I'm not... that dumb..." She rubbed at her cheek a moment before she hopped down just in front of Sunburst. "Just, you know, what I could have done, but didn't... Don't you have those kinds of regrets?"
"Too many to count," half-laughed out Sunburst, a little smile on his face. "Hey, look, we can't change the past, but we really are in the middle of a big project, and I really think you'll enjoy being a part of it."
Moon inclined an ear to the side before perking both up, studying him a moment. "On a level of 1 to 10, how complex would you place this endeavor?"
"10 for comprehension," easily admitted the stallion. "The actual process.... 8-9? Mostly in the 'how do we do this in a way that won't kill or maim ponies' way. I mean, we could wipe all horn spurs from existence if we wanted, but not with any good results to those carrying them."
Moon rubbed along her chin with the flat of a hoof. "You rate the comprehension higher? Fascinating... I'm pretty good at deciphering text." She set her hoof down and stood up. "We'll figure this out."
With a growing smile, he pat her shoulder. "Fantastic, good to have you on board."
"We'll find a solution in no time," came a sudden new voice, Twilight leaning over the side of the bed, looking at the two of them with a bright smile. "With Team Celestial, how can we fail?!"
Moondancer tilted her head. "Team Celestial?"
Sunburst got it with a smile. "We're all named for celestial things. We have Twilight, Sunburst, and Moon Dancer. Day, night, and what comes between."
Moondancer looked between Twilight and Sunburst. "That... describes the situation far too uncannily. I do not usually subscribe to the idea of a forced destiny, but this makes me reconsider... Thank you, both of you. Let's put our intellect to work."
Their hooves met in a three way bumping. It was time to start the day. Showers were had, breakfast was eaten. Parents were said goodbye to with warm hugs all around.
The trio made good time through the city, only pausing to buy tickets at the station. "Don't even worry about it," assured Twilight as she purchased all three for them. "This is our idea, we're not going to make you pay for the ride."
Soon they were on the train. They didn't get a private car, instead just sitting with everypony else. Sunburst and Twilight were side by side, with Moon across from them. Sun was watching the scenery as they descended the mountain. "You know, a small part of me wonders what the odds are each time, you know, of the train just careening off the tracks while we're this high up."
Twilight nudged him with a snort. "That isn't going to happen."
"Not technically true." Moon adjusted her glasses much as Sunburst had the habit of doing. "According to historical data, there is a 0.2% chance of that event occurring, working entirely on a probability basis on how many times it's actually happened."
They were both staring at her, a little stunned. "What? An average of 500 trains passes over these tracks without incident. Safety measures usually minimize the injuries on the 500th train. I can only recall one incident that had the train actually make the entire trip from the tracks to the ground." She pointed a hoof down at the ground so very far below them.
Twilight swallowed heavily. "Oh, well... that's good at least... Let's hope we're not train #500." She and Sun leaned in closer, sharing in their short-lived fear of crashing train cars.
Thankfully, the train did not have an unkind experience with gravity that day. They made it to Ponyville, all their hooves where they should be.
Only Moon has anything to carry with her, and it was just the bag she had at her side, so they departed the train smoothly when it arrived, spilling out with the other ponies onto the station platform.
"Twilight!" came an excited cry, Pinkie waving wildly. "Over here!"
Twilight smiled at her excited friend. "You're not that far away. I can see you. Pinkie, this is--"
"Moon Dancer, we've met." Pinkie thrust a hoof out towards Moon and it was met in a soft clop.
"Ah, right, I forgot. That's one friend down. She's going to be stay--"
"--I'm on the case!" Pinkie saluted and dashed off so fast a pony-shaped cloud was left behind.
Sunburst chuckled softly as he walked towards the exit. "You'll be getting a party shortly, be ready for that."
"She made fast friends with my other compatriots." Moon followed after Sunburst, Twilight after her. "I expect the same level of extroversion."
Twilight gave a single powerful 'Ha'. "She makes Minuette look like a shut-in at times."
Moon perked an ear back at Twilight. "How do you survive?"
Sun stepped to the side, holding open a door with his horn. "She makes really good cake."
"Ah." As if that explained the great balance that was in effect. Together, the trio ascended up towards the castle two of them had started from. "So this is yours? It's.... big."
Sun nodded in agreement with Moon. "My thoughts exactly."
Twilight blushed softly as she approached the doors. "I didn't get to choose how big it was, it just... happened. She willed the door open. "Spike, Starlight? We're back!"
Moondancer trotted up with the others, entering the crystal palace. "Oh, are those your things?"
There was their luggage, stacked just inside the door.
Twilight rolled her eyes. "I had hoped somepony would put them away, but that works." She whisked her luggage away with a pop of magic. "Spike? Hmm. Oh! Today's a school day. Those two are busy being responsible and here I am, shouting for them."
Moon glanced in the direction of the school. "Ah, yes. I would like to visit that."
"You could guest-lecture, if you're feeling up for it." Twilight trotted towards the kitchen at an easy pace. "I'm sure you're full of interesting facts the students would love to hear."
Moon tried to hide the flinch that came on her. "I'm not... I don't have a syllabus ready."
"It's ok." Sun bumped into her from the side. "Once you do it once, it comes naturally, honest."
"If you say so..." She scurried after Twilight. "This looks homey..." The kitchen was downright cozy compared to the cool crystals of what she had seen. "I don't normally think of decorations, but this is nice."
Twilight turned away from her fridge back towards Moon. "You can thank my friends for that. They really went out of their way to make the castle more like home. The kitchen is one of the bright points for sure."
Sun did not enter, grabbing a banana from outside, floating along in his magic. "Did you want to see what we're working on?"
"Please." She set her bag aside casually. "That is why I'm here." None of the three were sure that was the only reason she was there, but it certainly was the reason they were going with.
"It's a real horn-bender, written in contrary debate thesis format." Twilight closed the fridge and trotted out with an apple, chewing on it as she walked.
"Ooo, a classic," Moon agreed as she followed. "Especially popular with authors that are unsure themselves of what results to draw from their research." She began to ascend the stairs towards the book with the others around her. "Though it did see limited popularity when writing about politically sensitive topics, where having a clear opinion for or against a given topic could result in a pony being jailed, or worse."
Sun shook his head as he climbed, the banana reduced to a peel. "I don't think there are too many political rammifications here."
"I disagree." Moon didn't slow or stop as she argued. "This is a book that says that magic is not simply a matter of 'good breeding' or 'bad breeding', but can be acted on and addressed, making a pony better at it after the fact. The idea could have been seen as quite controversial at certain times of history."
Twilight raised a hoof to her chin as she walked. "I hadn't considered it from that angle before. You could be onto something there. I'm already glad we brought you in." With a smile, she opened a door with her magic. "Here is our project room."
Moon advanced past Twilight, examining the room critically. "Mmm." She saw the book, the massive tome that had defined their life for the last few months. "Oh. This is a big one." She approached more cautiously, as if stalking the book. "You've made considerable effort." It wasn't hard for her to see the heavy bookmark that noted where they left off.
Sun closed the door behind them. "It's been a passion project for a while, yes. We have one technique published and being tried on actual ponies, but we aren't done. We could find better ways that can help more ponies with this issue."
Moon looked up sharply at Sun. "You didn't finish and you published?! That's... reckless... to say the least."
Twilight raised a hoof. "I will accept the responsibility. It's only applicable to foals, but it seems like a real winner for them at least, if they are diagnosed early enough. The trick is requiring that they be diagnosed, which is far from assured... Some ponies just mature into magic later, and that's perfectly normal."
Sunburst bobbed his head. "That's what my mother thought, even as she sent me off to school... That I'd 'get better' as I practiced more and more. Um, well, I guess I did, a little... but..."
Twilight crossed to him quickly, setting a hoof on his shoulder. "You are an amazing wizard, Sunburst. Let's finish figuring out how to make you an even better one."
Moon swiveled an ear off to the side. "That lines up with what I had observed of you..." Her wandering eyes spotted a paper and she willed it up into view. "Is this you?" She was holding the diagram of Sunburst's horn, spurs nakedly visible. "Fascinating..."
"Speaking of that. If you would sit down, I'd like to add your horn to the collection." When Moon's eyes widened, Twilight laughed. "I just mean a drawing, like this. I promise your horn will be entirely unharmed."
"Oh, of course." She blushed softly at her foalish misunderstanding. "When you're ready." She sat down lightly. "What is the average time to completion?"
Sun shrugged lightly. "It took us about five minutes? But Twilight's had practice now, maybe a little less?"
"I'm already on it." With a glowing horn, she began to explore Moon's horn, a new paper with a fresh quill starting to fill out with an interior view of Moon's horn.
She was officially part of the research effort.