Outside, it was a good day. The sun was shining, it was the middle of spring, there wasn't a single cloud in the sky, and the many parks scattered around Canterlot City were graced with a pleasant easterly breeze that boosted the conditions from 'acceptable' to 'absolutely perfect'. Parents the city over found themselves host to renewed headaches at the insistent whines of their offspring to be unleashed upon such fortuitous outdoor conditions.
Even the Princess herself, normally confined to the interior of Canterlot Palace during the afternoon hours, had elected to relocate the Solar Court to the castle grounds, much to the consternation of the unicorn nobility. Laughter and cries of merriment, coupled with the occasional beat of a singing flash mob, echoed from all corners of Canterlot as what seemed like the entire population filled the streets, enjoying the day.
It would come as a surprise to most, then, to discover that at least one of the city's inhabitants was not outside, but had instead opted to inhabit the Canterlot Castle Library. A stuffy, dark, cold place at the best of times, the Library could not have been more opposed to the vibrant conditions that now enclosed it. To any sane pony, depriving themselves of such a radiant outdoor environment in favour of the library would be considered an act of lunacy worthy of incarceration in any of Equestria's fine mental institutions.
To those that knew anything about her, however, the library's current inhabitant's presence was not particularly surprising. While many would consider it strange in the extreme, her preference for the solitude and quiet of the library significantly outweighed any desire to partake of the afternoon's glow. In fact, given that everyone else in the city was outside doing exactly that, her preference for partaking of the library had been only strengthened, since it meant she was now alone in the greatest repository of knowledge in Equestria, surrounded by the (to her) intoxicating smell of dust and old paper, a first edition of Niccolo Marechiavelli's The Princess open in front of her.
Twilight Sparkle was in heaven.
Well, that was her intention, at least. Upon waking to discover the day's climatic wonder she had almost shattered her bedroom window with cries of glee, realising that everypony would be outside today, leaving her free and clear to partake of the normally-crowded library. In fact, it had been the reality up until a few seconds prior, when her attention had wavered from the tome before her for an instant, drawn outdoors through the library window.
The library, uniquely among libraries, had an unparalleled view of Canterlot Palace and its surrounds. Twilight had often entertained the prospect of taking her telescope and using it to observe the comings-and-goings of the many visitors to the Palace, but had never had the opportunity to execute the idea, owing to the library's typical patronage. She was rather annoyed that she had failed to remember the idea in her haste to appropriate the library for her own ends. It would have provided her with a much easier time of attempting to identify the distraction.
It was a pony, that much was clear. They were purple, as far as she could tell, but then a purple coat isn't all that remarkable when you live among a population of creatures whose range of colours were seemingly endless.
Beyond that, she could discern nothing specific about that particular pony from that distance. Other than the fact that they seemed wrong.
And she didn't know why.
"Strange," she muttered to herself, abandoning the ancient tome in front of her in favour or leaning closer to the window, trying in vain to distinguish further details. "Who are you?"
The question echoed around in her head for minutes as she watched the pony wander through the castle gardens, pausing occasionally, she assumed, to partake of the garden's many fragrant flowers, or to greet the occasional passer-by who happened to intersect the mystery pony's path. Her frustration only grew at attempting to identify the strange characteristic that had drawn her initial attention, only to come up with nothing.
A chill ran through her nose as it pressed up against the window glass, momentarily startling her before she realised she had unconsciously moved herself closer, her hooves likewise pressed against the glass in a vain attempt to close the distance to the object of her curiosity and identify it.
With a groan, she pushed herself away from the window, shaking her head in an attempt to clear her mind and refocus on her initial intention of the day, to read her book.
"It's just a random pony enjoying the day," she muttered to herself, trying to find where she had left off. "Just like anypony else. Out, enjoying the day, strolling through the gardens, absolutely nothing untoward, nothing strange, just a normal, regular pony."
She grit her teeth, steadfastly boring her glare into the book, denying the insistent, nagging urge to divert her gaze back out of the window. Small beads of sweat began to collect around her mane as she forced her attention towards the book.
It wasn't until she had read the same sentence six times in her attempt to resume that Twilight finally abandoned the attempt, batting the book closed in frustration before once again turning her gaze outside, slamming her hooves against the glass.
"Why can't I stop watching you?" She cried, face pressed uncomfortably against the glass as she watched the purple interloper. "Who are you?"
She froze in place as the mystery pony turned and looked right back at her. Normally, given the distance, she would have doubted her ability to determine the direction of the pony's perception beyond vague directions, but in that instant, she knew that the pony down there was looking right at her. And they knew that she was looking right back.
The pony bolted.
Twilight squeaked in surprise, watching the pony dart through the gardens, dodging ponies and bushes alike as they made a hasty beeline for the exit. Others turned to regard the running pony with what she could only assume was confusion at the sight of anyone running so determedly through the gardens.
For a moment, she entertained the possibility of simply letting the pony go, conjuring dozens of potential mundane explanations for their sudden departure, any one of them as plausible as the last. They were late for an appointment and had only just seen the time. They were playing a game of chase with their children and had been spotted. They were being chased by a swarm of killer bees.
The moment passed quickly, however, before she resolved herself to pursuing the mystery pony and discovering their secret. Plans formed in her head as she surveyed the gardens, vainly attempting to calculate a route that would get her from the library to the gardens before her quarry had a chance to escape.
For a normal pony, it would have been impossible. Even a pegasus would have been hard pressed to find an appropriate, safe path from the lofty library to the ground. For Twilight Sparkle, student at Celestia's School for Gifted Unicorns and head of her class, it was a trivial exercise.
The world tilted sideways, the muted browns and blues of the library interior replaced with the vibrant colours of the outdoors as she teleported herself to the grounds. A sharp jolt of pain seared through her horn at the sudden discharge, reminding her of the need to practice that particular spell before using it so flippantly.
"Twilight!" Came a voice from behind her. "You're outside! Certainly wasn't expecting that today."
She turned, regarding the pony with a mild detached annoyance. It was one of her classmates, insisting once again on superfluous, unnecessary social interaction when there were far more pressing matters at hoof.
"Sorry," she said, smiling falsely as she whipped her head around, trying to locate her quarry among the crowds. "Bit busy at the moment."
"When are you not busy?" Came the reply, dripping with sarcasm.
Twilight didn't bother to respond, instead darting off when she saw the barest hint of purple out of the corner of her eye near the garden's exit. A cry of indignation followed her sudden departure, but she paid it no mind, her attention solely focussed on the matter at hoof.
A task made all the more difficult by the crowded, bustling streets of mid-afternoon Canterlot. She grumbled, pushing through the crowds in pursuit of her target, trying to close the already-considerable gap between them. Ponies around her grumbled as she pushed past them, nearly colliding with a few of them in her haste.
"Agh, where are you?" She muttered, craning her head to try and see over the crowd and spot her target. A quiet exclamation escaped her as she spotted them dart into an alleyway a few hundred yards ahead of her, only to be snuffed from her lungs as a passer-by forcefully collided with her, sending them both head-over-hooves in a tumble of purple and white.
"Ow." Twilight moaned, trying to extricate herself for the tangle of limbs and bags, glaring at the alabaster unicorn that had collided with her.
"Oh, I am so sorry dear!" She replied, pulling away from Twilight with an apologetic look on her face. "I was miles away, didn't even see you there."
"Watch where you're going next time." Twilight growled back, rising shakily to her hooves. "Some of us don't appreciate being bowled over by every Canterlotain who decides to clog up the streets."
"Oh, I'm not from Canterlot, I'm just visiting from Ponyville. Though I do hope to live here one day." She explained, extending a hoof in greeting. "Besides, where are my manners? My name's Rar-"
"Don't care." Twilight interrupted, swatting the hoof away in annoyance before dashing off again, leaving the unicorn grumbling as she collected her bags.
The crowd slowly thinned as she reached the alley, ponies stepping aside as the near-frantic unicorn dashed toward the entrance. She darted inside, panting at the exertion and scanning the alleyway for the mystery pony.
It was empty.
"Oh come on!" She groaned, trotting forward into the inky darkness. "All that and they're gone? Typical."
She continued forwards, lighting her horn to try and banish the shadows, only to reveal more empty alley. Another groan escaped her lips as her frustration grew further.
Exhausted, she took the opportunity to lean against a hay bale that had been left near the rear entrance to a nearby store, trying to steady her breathing.
Something in the darkness beeped.
Twilight froze, her ears twitching as she tried to localise the source of the noise.
Something beeped again.
She crept forward, trying to keep her hoofsteps as silent as possible as she closed on the noise. Her heart hammered in her chest as excitement coursed through her system, drumming a tattoo that she was entirely sure could be heard for miles.
"C'mon, there's enough room here!"
Twilight stopped again and dropped to the ground, holding her breath in fear and extinguishing the light on her horn. She crept forward on her hoof-tips, barrel scraping the cobblestones painfully.
Another beep echoed through the alley, followed by an annoyed exclamation.
"Oh Celestia damn it!"
Twilight tilted her head in confusion. The voice was oddly familiar, yet had a strange quality about it that she couldn't identify. She continued to creep forward, keeping herself hidden behind a stack of boxes as she approached the voice's source, only to find herself in a pile of hooves for the second time that day as the mystery pony barged back into the alleyway, running headlong into the hidden Twilight.
"Owwww." Twilight groaned again, struggling in vain to free herself from her quarry. "Why do people keep running into... me..."
The complaint died in her throat as she looked up and into the face of the pony she was pursuing, only to see herself staring back with a look of horror on her face. Experimentally, she tilted her head marginally and flicked her ears, expecting the face in front of her, her face, to do the same.
It didn't.
Not a reflection, then.
"Not possible." Twilight muttered to herself, her faculties for more complex language having evidently vacated for the time being.
Her duplicate stared down at her in horror, apparently at a loss for what to do next. "Okay... This is... bad."
Twilight reached out a hoof, tentatively poking the duplicate to check if it was solid or merely a hallucination brought on by what she expected was stress exhaustion. To her dismay, however, it was solid.
"Yes, I'm real." Her duplicate snapped.
Twilight yanked her hoof back, only to have it catch on a chain hung around her duplicate's neck, upon which a small pendant hung.
"Ah, careful!" The duplicate cautioned, alarmed. "Don't touch-"
Twilight's hoof grazed the pendant, triggering a light whistle. The pendant's edge began to glow green, pulsing gently.
"-that." She groaned. "NOW you work? at the worst possible moment? Celestia above..."
"Sorry." Twilight offered, at a loss for what to say.
Her duplicate just glared at her, an exasperated look filling her face.
A small ding issued from the amulet as the green pulse turned solid. An instant later, Twilight felt the bottom drop out of her stomach as the world lurched sideways.