"Aaugh...!"
Starlight collapsed to the floor, clutching her head as a mixture of pain and memory flooded it.
Sunset. The orange pony had been Sunset Shimmer. She could remember that much, now; Twilight had messaged her through that book thing and asked her to help with the spell testing, since they had both been Celestia's students.
"Starlight!"
But what was she doing here? Did that mean Twilight was floating around somewhere, too? With any luck, if Sunset had the insight to come looking for the library, so would she.
"Starlight, are you okay?"
But that wasn't all she remembered. There was still a blur surrounding the actual testing, but something else that hadn't even struck her as odd before now stood out clear as day - something about her time here so far that should not have been. The realization sent a chill down her spine.
"Come on, say something. Tell me you're alright."
Distracted as she was, Starlight hadn't noticed Sunset rushing to her side until she felt a hoof gently brushing her coat. Panting, she realized the headache had begun to ebb, and slowly sat up.
"I... I'm fine, I just... need a minute," said Starlight. A few deep breaths later, the pain had calmed enough for her to start getting her thoughts in order. "The... the spell. Sunset, what did we do wrong?"
Sunset shook her head. "I was going to ask you that. I thought you said it wasn't supposed to be for travel."
"It wasn't," said Starlight. "This shouldn't have been possible. You saw it yourself; it was only supposed to create a viewport into the past, not a doorway. Nothing on that scroll should have been able to do this."
"Should have," echoed Sunset, "but here we are anyway."
"We..." Starlight took a deep breath. "But if I was the one testing the spell, why are you here too?"
Sunset quirked an eyebrow. "What, you don't remember?"
Now it was Starlight's turn to shake her head. "Digging for details just makes the headache worse."
Sunset sighed. "When I saw the spell going haywire, I rushed in to help stabilize it. Obviously it didn't work."
"What about Twilight?"
"She stayed behind cover the whole time, because clearly unlike me, she's not an idiot."
While Starlight was of course relieved to hear that her mentor hadn't gotten herself caught in the spell, it also meant she wouldn't be there to help them find a way back. Her heart sank; apparently she wouldn't be relying on either Twilight to help her out of this mess.
She sighed, a timid smile creeping onto her face. "Well, I'm glad I'm not the only one, at least."
Sunset rolled her eyes. "C'mon, don't do that to yourself."
"What, so you're allowed to, but I'm not?" Starlight's smile quickly faded. "It's my fault we're even here to begin with, remember?"
Sunset smirked. "Yeah, and I'll make you eat those words when you fix the spell and get us back home."
Starlight felt a familiar chill. "I'm... not sure it's going to be that easy, Sunset."
"Well, not with that attitude."
"No, I don't think you understand." Starlight turned away. "I think that spell did more than just displace us on the timeline. I... I think it affected the timeline itself somehow."
Sunset stared blankly. "Um, what? How? And how do you know?"
"Well..." Starlight paused for breath and turned back around. "What can you tell me about when we are based on what you've observed so far?"
Sunset sat back on her haunches, raising a hoof to her chin as she processed everything. "Let's see... well, the girls at Canterlot High hated my guts when I tried talking to them, so we're... a year back at least? I wish I had thought to check the prom queen pictures before I left; I was in kind of a rush to make sure the mirror portal was open. Then again, that's assuming the passage of time is consistent between the two worlds, and I never really had the opportunity to test it..."
"It's worse than that," said Starlight, her ears drooping. "The library is here, but Twilight's not in it yet, so... Try something more like several years."
"Okay." Sunset glanced around the room for a moment. "So, worse than I thought, but I'm not seeing the catastrophe yet."
Starlight cleared her throat. "When I awoke after the time spell, I was back in my village," she said slowly. "Do you remember when I told you that story?"
"Oh yeah," said Sunset, "I do. You had that whole cutie mark equality thing going, didn't you?"
Starlight nodded. "I led that village for just barely a year before Twilight and her friends arrived and disrupted everything."
"Okay," Sunset repeated. "That all makes sense to - "
Starlight would have sworn she had heard an audible 'click' as Sunset's brain connected the dots.
Sunset scowled. "Wait a minute. That's impossible."
Starlight nodded and smiled, her ears still folded back against her head. "Not only that, but I set the villagers free before I left, and some of them said they'd been there too long to have a home to go back to anymore. If that's true, the village is likely already a few years old at least."
Sunset paused for several moments before finally heaving a noisy sigh. "I'm surprised I don't have a headache like that too. Ugh, I hate time travel."
Starlight winced. "Sorry for getting you caught up in all this, Sunset..."
"No, I didn't mean it like that." Sunset shook her head. "Forget I said anything. Come on, let's get that spell back down on paper so we can find a way to fix it."
"Is that it?"
The two unicorns stared at the scroll. Though it otherwise stretched the entire length of the parchment, there were several large gaps in the script.
"That's all I can remember without too much pain," said Starlight. "Any more might come at the cost of my head splitting open."
Sunset frowned. "How are we supposed to find the flaw in a spell if we've only got like, eighty percent of it?"
"I'm sorry...." Starlight clutched her head again. "I really don't know what's up with this headache, but it's making this so much harder than it needs to be."
"Stop apologizing and just rest for a few minutes, Starlight," said Sunset as she trotted over to the bookshelves. "I'll see if there's anything here we can use to fill in the gaps."
"Well go on already!"
Sunset opened her mouth to reply, only to realize the voice she'd just heard was too muffled to be Starlight. Instead, it seemed to be coming from outside the front door.
"I have to wait for the proper dramatic moment!" said a second voice. "There's a rhyme and reason to these things, you know! It's not every day you run into an honest-to-Celestia time traveler."
There was a sigh. "Doctor, please, this really isn't the time! She needs your help!"
"Oh very well," the second voice conceded.
Sunset quirked an eyebrow and backed a couple of paces away from the door a second before it opened to permit a pair of ponies.
"Starlight? Oh, there you are!"
Starlight's eyes lit up. "Oh, Derpy, you're back!" She waved Sunset over as she trotted up to meet them. "Is this the friend you mentioned?"
"Mhmm!" Derpy nodded vigorously. "I'd like you to meet Doctor Whooves. Doctor, this is Starlight Glimmer, and... uh?" She tilted her head, clearly puzzled by Sunset's presence.
"This is Sunset Shimmer, a... colleague of mine. She showed up just after you left," said Starlight. "It's nice to meet you, Doctor! Derpy really talks up your expertise."
"The pleasure is all mine, I assure you!" Doctor Whooves grinned as he briefly bowed his head in greeting. "Are the both of you time travelers, then?"
"Not intentionally," said Sunset. "The spell that brought us here only did so because it went haywire. It wasn't supposed to send anyone through time in the first place."
"Hmm. Well that's a problem then, isn't it?" The Doctor's brow furrowed. "Let's have a look at the spell in question, I suppose. Have you got it with you?"
Starlight directed the group over to the desk where the incomplete spell sat, grasping it in her magic and holding it out for the Doctor to read. "Just what we could recreate from memory."
A couple of minutes passed by as he studied the contents of the scroll. "Fascinating... Did you write this yourself, Miss Glimmer?"
Starlight nodded. "Yeah, actually. How'd you know?"
"The only other unicorn I know who was brave enough to experiment with temporal magic was Starswirl the Bearded, and this isn't anywhere near his style of spell writing." He rubbed his nose as he pondered the spell some more. "So this was... an aperture?"
"Yeah." Starlight sighed. "It was supposed to allow the viewing of past events at the location it was cast, without affecting anything at the destination in the process."
"This segment here," said the Doctor as he pointed to a large paragraph near the bottom, "is this a dimensional spell lattice?"
Starlight nodded again. "I added that so I could manipulate the angle of the aperture at the far end. That way, the caster would have a full range of vision in all directions from the target location."
"Fascinating indeed...!" The Doctor's grin returned. "I imagine all this would have taken one doozy of an activation matrix to properly regulate the energy flow, but..." He trailed off, pointing to an empty portion near the top.
Starlight bit her lip. Her brain simply refused to yield that portion of the spell to her, no matter how hard she tried to remember.
"Still, this is some impressive spell work," said the Doctor. "What you've created here is hardly a mere time spell. It's more of a... time-and-relative-dimension-in-space spell!" He looked pleased with himself for about two seconds. "Oh, but that rolls off the tongue rather poorly, doesn't it...?"
"I don't think it matters what we call it," said Starlight with a sigh. "Unless this podunk little library somehow has a book on advanced activation matrices, I don't think this incomplete spell is going to get us anywhere."
"A book like that would have to be in the Canterlot Archives, probably in the Starswirl wing..." Sunset brought a hoof to her muzzle in thought. "...but that section requires clearance none of us have."
Starlight blinked. "Wait. You were Princess Celestia's student though. Don't you have clearance?"
"I did, yeah." Sunset huffed. "But she almost certainly revoked it after I rejected her as my mentor and ragequit Equestria itself."
"Rage... what?"
Sunset shook her head. "N-Never mind. I mean when I left through the mirror portal."
"Oh."
Derpy grinned. "Hey, that's some great timing then! You can ask her about it tomorrow!"
"Tomorrow?" asked Starlight and Sunset in unison.
"Yeah! The Summer Sun Celebration's being held in Ponyville this year, so she'll be in town for a few hours," said Derpy.
Sunset blinked. "Well, I'm not looking forward to confronting her again, but... if that's what we need to do to fix this thing and get home, I'll do it. What do you think, Star - ?"
Sunset stopped mid-word as she caught sight of Starlight's face. Her eyes were wide as dinner plates, the pupils shrunk to pinpricks, and her ears were pressed flat against her head.
"No..."