Sweetie awoke to a multicolored light seeping through her eyelids, and the smell of dust. At first she remembered nothing of recent events, and groggily wondered why she didn't seem to be in her bedroom. Then she remembered her frantic flight through the woods and started, opening her eyes.
"Hello, Sweetie," Twilight's voice calmed her, and she finished her sit more calmly than it began. She looked around. She was in a room she didn't recognize, though appropriately to Twilight, the walls were covered in dusty tomes, their smell permeating the room. The strange light she'd first noticed was caused by the sun entering through two stained glass windows, one midnight blue the other a warm yellow-orange. If Sweetie hadn't explored Twilight's new castle a few days ago, she'd have thought this must be it. She looked over in the direction of Twilight's voice and saw the Princess lying on a pillow in the corner, book open in front of her.
"Is this the castle in the Everfree?"
"That's right," Twilight smiled at her, "well done, Sweetie. It's proper name is the Castle of the Two Sisters, though it's seen better days. This is one of the few intact rooms left above ground. Thankfully, Luna and Celestia had their priorities right even back then, and made sure the library was nearly indestructible."
"Why'd you bring me here? And did you have to fight those weird ponies?"
"Well," Twilight frowned, "that's just the thing, we couldn't find anything chasing you at all, when we went to look."
"But, they were there, I promise! A bunch of ponies with creepy blue eyes, and they didn't move right."
The frown deepened. "I believe you, Sweetie, and I want to hear all about it in a bit, but let me answer your question first. The Everfree's full of strange things, and we didn't know what had spooked you so much. I was worried you might have some magical malady that wouldn't be obvious right off. Like the poison joke, which takes a little while for symptoms to show. I was on a pretty tight timetable to get these books, so we brought you along. Don't worry, I sent word back to your sister and parents that you're okay and with me."
Sweetie imagined herself back in Ponyville, seeing blue-eyed specters around every corner, jumping at shadows...only for Twilight to come back and tell her it was all in her head, the result of some forest spell. She twitched a little.
"Don't worry," Twilight said, "you seem fine to me. I used a minor sleep spell to make sure you got a good rest, and checked you over for hostile magic while you did. Nothing's out of the ordinary. Whatever you saw was certainly real," she sighed. "Of course, that just raises other questions. I've never heard of a creature like that before. There are a lot of things living in the Everfree, so I'm not too worried, but it's always a bit concerning when something looks like a pony. I'll add it to my research list, maybe there's something about it in all this stuff!"
"Err...thanks?" Sweetie wasn't sure whether to be reassured or not, but at least she was safe.
"What were you doing in the forest, anyway?"
"Oh, right! I was looking for you! We've all been looking for you for a few days now." Twilight tilted her head, and Sweetie pressed on. "We all want to write a book about you and how you became a Princess! But I have a question for you about unicorn magic and cutie marks, too."
"Oh, well, I'm flattered you girls want to write my biography," Twilight smiled, "but that's a big job, we'll probably have to set aside a time when I can talk to all of you for at least a few hours, and when you're ready to take notes. But I can talk to you about magic now, if you like."
"Yeah," Sweetie blushed, "I mostly wanted to talk about that. I mean, I do want to write it with them, but I knew we'd need all of us for that. There's something with my magic that's been bothering me for days, though." Quickly Sweetie told Twilight about the Crusaders' visit to the castle, her experience with the Alicorn Amulet, and the nagging feeling she'd had there was something she was supposed to do.
"Well," Twilight seemed to be trying to keep her face neutral, but her eyes twinkled a little at the opportunity to lecture, "cutie marks are one of the great remaining mysteries of magic. The spell that eventually transformed me into an alicorn, Starswirl's last spell, related to them somehow, and when it went wrong it scrambled up everypony's cutie marks, you might remember. Other than that, I've never heard of anypony being able to change or work with them, and that spell messed everything up when it did. When I first became Celestia's personal student, my mark was on my mind, since I'd just gotten it, so I asked her about it, and even she doesn't really know anything. She has one herself, after all, and got it just like the rest of us, when she first realized she could control the sun alone. It's different for everypony, and every type of pony too. She made it my first research project to interview some ponies about getting their marks, and most of the unicorns described something like Rarity or I had, where they felt a lack of control, or a kind of possession by magic. At the time, my theory was that because unicorns tend to be...a bit particular, the first contact with our life passion brought us out of ourselves in a way that was really memorable. Now I'm not so sure. I think talking mostly to my fellow students selected for a really organized nature. Now I've met unicorns who are less so, like you or Lyra, and Lyra certainly felt something similar when she got her mark, and it sounds like you've been having a similar feeling lately. So maybe there's something else to it, like our more direct control over magic gives us a closer connection to the purposes that control cutie marks, and so we can feel something more of them than pegasi or earth ponies."
Sweetie blinked twice. She thought she'd gotten some of that, but about two-thirds of the way through she'd drifted off and started thinking about Celestia learning to control the sun, and by the time she'd gotten over her vision of herself as a dashing young Princess, all dressed in gleaming armor, learning she could do what had previously taken a whole council of the most powerful unicorns, Twilight was looking at her expectantly.
"Uh, that's neat Twilight, but what should I do? You just cast a spell out of nowhere and got your mark, Rarity knew just what she had to do to follow her magic. I just had this weird feeling that something was up, and this creepy feeling like something's not quite right. It's not fair!"
Twilight got to her hooves and walked over to lean against Sweetie.
"I know, you're right," she wrapped a wing around her, "it isn't. I wish I knew what to tell you. But putting on the Alicorn Amulet isn't safe, and it seems like that's not what you want to do anyway." Twilight paused for a bit, then sighed. "To be honest, I felt something a bit strange myself when I went down to check it out later that day. I couldn't put my finger on what it was, so part of what I wanted to do here was research it. If you felt something strange too, it might be related to your mark, but it might also just mean you have stronger magic than we thought, or that it's focused in a way that's useful here, like detection, or divination, or something involved in making the amulet."
"Oh," Sweetie drooped, then perked up, "but if I did have magic that's really focused, it might be related to my special talent and my cutie mark, right?"
Twilight laughed. "Yes, it very well might. Certainly my guard unicorns haven't mentioned anything unusual about the basement or the Amulet, and I only felt it slightly, it sounds like no stronger than you did and maybe even weaker. Since alicorns are so much more magically sensitive and powerful, that says a lot." She grinned wider at Sweetie's eager look. "How about you help me look into this? I'm not really comfortable sending you home through the forest alone," Sweetie nodded at this, eyes wide, "and it'll take the guards at least a day to gather all this stuff up and pack it. We might not get back much before Applejack's reunion. What if you helped me do some research while you're here?"
"Wow," Sweetie said, "like your own personal student?"
"Well, let's not get ahead of ourselves," Twilight laughed, "I don't even have a school, and I have no idea yet if my duties will let me take on a long-term student. But I was already teaching you magic, and if you do have special skills, I can't think of anypony else in Ponyville who could do it. I wouldn't be much of a Princess of Friendship if I made you choose between learning to use your talents and staying with your friends, would I?"
Sweetie shook her head enthusiastically. "Not much of one at all."
Twilight smiled at her, removed her wing, and started towards the bookshelves. "Well, we wouldn't want that. Let's get started."
Sweetie'd always secretly had a bit more of an attention span than her friends. While she wasn't always the fastest of them on the uptake, she found that study suited her - she took a while to get going, but once she got enough information to start forming a picture of the thing as a whole, she could reach a complicated understanding. Cherilee alternately praised and lamented this talent, depending on how much she'd let her friends disrupt it over the course of any particular assignment.
Sweetie of course loved them dearly, and was confident they made her a better pony, but just for now, her friends' absence was a blessing. Free of their impulsive influence, she barely noticed the hours fly by as she sat next to Twilight, painstakingly cross-referencing in the old tomes, trying to link the passages her tutor showed her. As the light through both of the stained glass windows tinted red, she finally felt like she was starting to get it.
"Oh! It's kind of like, this part goes here, and this one goes here," she muttered, not really directed at Twilight. She barely noticed her horn beginning to glow as she lined up a section of runes from one of her note cards with a similar section from another. A section six characters long was indeed the same, and the page was briefly bathed in green light as her eyes and horn flashed. She blinked, and when she opened her eyes, the whole room was overlaid with motes of light, multicolored, looking like nothing so much as festive dust motes dancing in an unseen sunbeam.
"Wow," she said, "Twilight, what's this?"
"That," Twilight beamed at her, "is First Law's Illuminator. First Law was one of the first unicorns to write down and codify spells, using those runes you've been working with all afternoon. I've never seen such a complete set of his writings before! That spell shows the flow of magic in your line of sight. In this room, right now, we're not doing anything very powerful, certainly not compared to the leftover magic from the construction and enchanting of the castle itself, so you just see the background magic drifting around like that. That's one of the first spells advanced magic students learn, and it's very useful when you're studying non-unicorn magic, where there isn't a telltale sign like the glowing horn to let you know what's going on. First Law used it to prove earth ponies and pegasus ponies had magic as powerful, if different, than unicorn magic, though sadly it took a long time before it was widely accepted among unicorn academics, and some are still ignorantly dismissive of non-unicorn magic even today."
"Aww," Sweetie said, "I thought you said we were learning new stuff! All that work and I just learned Baby's First Divination?"
Twilight snorted. "I said it was one of the first spells advanced students learn, I didn't learn it until my second year under Celestia and it took me a few days, you did a great job. Besides, that's just the first step in what we're doing, and I hadn't made it yet either. Nopony learns that spell like that anymore, we all learn it on our own, by example or in modern Equestrian. These books we've been looking at form First Law's Unified Theory of Magic. I've only ever heard of it in history books before, and I didn't know there was any of it left! Of course, we can't tell if this set is complete yet, but if it is, I'm hoping it will reveal links between different kinds of magic that we've forgotten about, and so ways to detect kinds of magic we can't see so easily by looking at their effects on what we can."
"Oh." Sweetie wasn't sure she'd gotten quite all of that, but blushed a little when she realized she'd learned something in day that had taken Twilight longer.
"Where did the runes tell you to hum like that, though?"
"What?"
"That tune you were humming when you cast the spell. I've never heard it before, I thought you must have gotten it from the runes."
"Uh...I don't think so. I didn't even notice I was humming."
Twilight frowned. "Strange. Let me see," she quickly scanned the runes looking at how Sweetie had lined them up. Her own eyes and horn briefly glowed, but she remained silent.
"Fascinating, that is a totally different way to form that spell than the one I learned," she muttered, then turned to Sweetie, "did I hum something and not notice?"
"Nope."
Twilight frowned briefly, then grinned. "Oh, this is a mystery, Sweetie Belle, and I do love a mystery! It's almost dark. We should relieve the guards and get them fed, and go to bed. I don't want to burn the magic to be up all night studying here, and honestly this library can get a bit creepy in the dark. But let's look into this more tomorrow. I'm hoping you can learn at least one more spell from these runes, and I'm really interested to see if you hum when you cast it. I've never heard of anything like that before, but it must mean something!"
Sweetie looked around nervously. Unlike Twilight, who was by this point supremely confident (not without reason) that nothing in this old castle could really threaten her, Sweetie found the mystery creepy. Her spine and coat tingled with discomfort at the idea that she'd been humming a melody she couldn't even recall as part of casting an old spell. She moved a little closer to Twilight, and breathed out in relief as she felt the Princess's wing around her.
"Oh, Sweetie, I'm sorry," Twilight said, "it's been too long since I was young and new to magic. You have to remember a unicorn's horn is...it's like at tiller for magic. You control it, you can use it to shape and move the flow of magic, but it works with something that isn't part of you, and runs deep and swift. When you're first learning real power, not the easy stuff like light telekinesis, it's a little bit scary because you don't feel like you're really in control. But I promise I won't let anything hurt you. Everypony manipulates magic in their own way. I'm interested in yours because it's unusual, but that doesn't mean it's weird or creepy. It might be the reason you seem to have so much more talent for some things that others. It's the good kind of mystery, I promise, and when we figure it out, it ,might reveal a lot about your special talent."
Sweetie's ears pricked up at that, and she managed a weak smile. "Okay Twilight, I believe you." Her stomach rumbled, and she suddenly realized she hadn't eaten since before her flight through the forest. "And I think I'm hungry now."
Twilight smiled, and the two walked off to the great hall to meet the guards.
After a satisfying meal, Sweetie found her fatigue catching up to her again. The guards built a large fire in the middle of the broken hall, open to the clear sky, and they clustered around it. The shadows among the old stones scared Sweetie for a little while, but Twilight lay down next to her with, of course, a book, and wrapped a wing around her again, and she felt safe, and drifted off into a deep sleep.
She slept soundly, and awoke refreshed, but she dreamed, or at least, she thought it was a dream, that the old stones of the castle were singing to her, in a language she didn't know, but could almost understand.