Twilight Sparkle loved many things. She loved Equestria, the beautiful land of her birth. She loved her friends, for all the smiles and warmth they gave her. And she loved her mentor, Princess Celestia, for the guidance and support she had provided over the years.

But none of this compared to the love she felt for getting lost in a good book.

Twilight lay on her bed, an imposing tome of ancient history open before her. Her eyes were bright as they skipped along the text, absorbing stories of ponies and nations long dead. She came across a particularly moving passage — a passionate speech delivered by a unicorn duchess, accusing the princess of violating the rights of the other tribes — and her wings fluttered softly.

Below, she could hear Spike softly humming as he tidied up, sorting scrolls and reshelving the odd book left lying open. The sounds of his activity were a gentle backdrop to Twilight’s studies, but her attention was pulled from the history of the ancient tribes when she heard a familiar sizzling belch.

“Twilight, letter for you from the Princess!”

“Be there in just a moment.” Coming downstairs, she saw Spike holding a scroll of fine parchment with Celestia’s seal. She took the scroll and unrolled it, her mouth moving soundlessly as she read.

My Dear Princess Twilight,

Over the past week, a number of troubling reports have reached me from across Equestria. It would seem that pegasi from every corner of our land are suffering some form of sickness, whose cause remains unknown. These pegasi all complain of the same symptom: a chronic weariness whenever they fly for an extended period of time.

It is therefore my request that you speak with the pegasi of Ponyville to determine if they too suffer this disease. If so, I also request that you attempt to study it, the better that a cure may be found.

Please keep me apprised of any developments in your study of this malady. I am deeply concerned for the fate of our land, and the sooner a solution is found, the sooner my mind will be at ease.

Always your devoted mentor,

Princess Celestia

P. S. Please show this letter to no one, and conduct your research as discretely as possible. I cannot explain further at this time, and must simply ask that you trust me.

Twilight read the letter twice more, her lips pursed. Spike stood patiently at her side, quill and parchment at the ready for her reply. Finishing her perusal of the letter, she rolled it back up and levitated it up to her bed. “Spike, take a letter please. Dear Princess Celestia,

“I would be happy to look into the problem you mentioned in your letter, and will begin my research at once. I trust you implicitly, and will promptly inform you of any discoveries. Your student, as always, Princess Twilight Sparkle.”

Spike finished penning the signature and looked up at Twilight. “Done. But what problem did the Princess mention? Is something bad happening?”

Remembering Celestia’s postscript, Twilight pawed the floor for a moment, casting about for an answer. “Oh, no problem... it’s just... Celestia wants me to look into something important. Y’know, princess stuff.”

Spike raised an eyebrow. “If you’re not supposed to tell me, you could just say so,” he deadpanned. “I’m not gonna go around blabbing the secrets of Equestria’s newest princess.”

Twilight frowned and placed a hoof on his shoulder. “Sorry, Spike. And yes, it is a secret. I’m sorry, but Celestia’s trusting me not to tell anyone.”

“Don’t worry, Twilight, my lips are sealed!” Spike pantomimed running a zipper across his mouth, then rolled up the scroll. He inhaled deeply and breathed out a green flame, which consumed the letter and carried it off to Canterlot.

Twilight giggled, patting Spike’s shoulder again. “Thanks, number one assistant. Now then, do you think you can manage the library for the rest of the day? I have a project to get to work on!”

As she walked through Ponyville, Twilight couldn’t help but dwell on the tone of Celestia’s message. In all the time she had known the Princess, she had never received such a letter; her insistence on secrecy, her mention of the fate of Equestria... It felt like her mentor hadn’t told her everything.

Trotting down Main Street, Twilight noticed she was drawing some glances from the surrounding ponies. She made sure her wings were tucked in tightly; her status as Princess still made her feel self-conscious. Her first few weeks back in Ponyville had been a huge embarrassment, with everypony she passed in the street scraping and bowing in her presence.

It wasn’t long before Twilight found the pony she was looking for. Scanning the sky, she spotted a colorful tail dangling from the edge of a low-drifting cloud. She smiled to herself and walked to the cloud’s other side to call up to the pegasus resting on it.

“Rainbow Dash, do you have a minute to come down and talk?”

Dash yawned and opened one eye. “Yeah, I was just chilling out after taking care of this morning’s weather. But aren’t you forgetting something?” Twilight simply blinked at her.

Smirking, Dash sat up and patted her cloud. “You can come up here now, remember?”

“Oh, right!” Twilight unfurled her wings, taking to the air with practiced grace and alighting gently on Rainbow’s cloud. “I keep forgetting I don’t need spells to walk on clouds anymore. Even after all the practice, I guess I’m still just a unicorn at heart.”

“You really oughta fly more, Twi,” Rainbow said, leaning back into the cloud with a small puff of mist. “You’ve gotten a lot better at it, and it was fun helping you learn. Besides, there’s nothing better than feeling the wind in your mane.” She fluttered her wings, gazing at them. “I don’t know what I would do without these babies. Anyway, what was it you wanted to talk about?”

“Well, about flying, actually.” Twilight said, sitting next to her friend. “Have any of the pegasi on your weather team complained about feeling unusually tired lately?”

“Uh, yeah, actually, they have.” Rainbow furrowed her brow. “A bunch of the pegasi in town have been talking about feeling worn out really fast whenever they fly. We’ve even had a few of the weather team members take sick leave. I figure it’s just some bug or something going around.”

“Do you remember when the pegasi first started feeling under the weather?”

“Maybe about a week ago? I’m not really sure.” Rainbow sat up again, her eyebrows raised. “Um, should I be worried about this?”

Twilight quickly smiled and waved a hoof. “Oh, no, just curious. Although, do you think you could do me a favor? If you could round up the ones who have been feeling sick and have them drop by the library this afternoon, that would be a big help.”

“Sure thing, Twi,” Rainbow Dash replied with a nod and a grin. “Are you gonna do some sciencey egghead stuff and make ‘em better?”

Twilight snorted, lightly batting Rainbow across the back with a wing. “It’s not ‘sciencey egghead stuff’, it’s research. But yes, I’ll be trying to find a way to make them feel better.”

Dash chuckled and knocked Twilight’s wing away with her own. “Same difference! But I bet if anypony can get them back in the sky, it’s you. And not a moment too soon. With my team getting sick, the weather hasn’t been so great lately.”

As Twilight prepared to depart, a thought struck her. “Say, Rainbow? You haven’t been feeling tired yourself, have you? No problems flying?”

Dash shook her head. “Nope, still tearin’ up the sky like always!”

Twilight gave her a smile. “Good. Make sure you keep yourself healthy, okay?”

“As if I’d do anything else! Don’t worry, Twi, I won’t let some pegasus bug get me down.”

Twilight glided back down to earth, suddenly feeling sure of herself once more. Perhaps Dash’s confidence had rubbed off on her. Soon she would speak with the ponies affected by this strange illness, and she had no doubt she could find a solution.

By afternoon, a line of pegasi stretched from the library’s door and down the street. Inside the library itself, Twilight sat at a simple desk, armed with the scrolls, quills and ink she would need to take notes from each pony. A red velvet cushion was positioned in front of the desk, to give each interviewee a comfortable seat. Spike stood by the door, waiting as Twilight double-checked her supplies. Finally, she gave him a nod.

“Okay, Spike, we’re ready. Let the first one in.”

Spike opened the door, greeting the first pony in line and motioning her in. Blossomforth poked her head in the door.

“Um, hi, Twili—uh, I mean, Princess.”

Twilight smiled. “Blossomforth, you know you can just call me Twilight. But come on in and take a seat.”

Blossomforth cracked a grin, stepping up to Twilight’s desk and sitting on the cushion. “Uh, thanks. Rainbow Dash said you wanted to talk to the pegasi who were feeling bad, right?”

“That’s right. And have you been feeling bad?”

Blossomforth shifted, scratching her head. “Uh, well... sorta? It’s kinda hard to explain. I mean, right now I feel perfectly fine, but whenever I try to fly... I dunno, I just get tired so fast.”

“I see,” Twilight replied, scribbling down some notes. “And how does it feel when you try to fly? Do you feel any kind of pain?”

“No, it doesn’t hurt at all. It just feels…” Blossomforth cocked her head, her tail flicking as she tried to describe her symptoms. ”Well, it’s like I feel heavier when I’m in the air. Like there’s a big weight tied to me. And I have to flap harder than I ought to just to stay airborne, which wears me out really fast.”

“Uh-huh...” Twilight continued writing, the scratching of the quill filling the momentary silence. “How long has it been since you started feeling this way?”

“Well, it’s only been a couple days for me, but some of the ponies on the weather team have been complaining about it for awhile now.”

Twilight looked up, her quill paused. “Oh? When was the first time you heard a pegasus mention it?”

“About a week ago, I think. Skytrail was the first one to say he was feeling tired, and he was also the first to say he couldn’t work the weather until he got better.”

Twilight nodded as she wrote. This corroborated Rainbow’s estimation of when the problem had started. “Okay. One last thing: have you talked to a doctor since this began?”

Blossomforth shook her head. “No, it hasn’t gotten bad enough for me to visit the hospital or anything. I think some of the ponies that took sick leave may have seen a doctor, though.”

Twilight scribbled down the last of her notes before looking up with a smile. “Thanks Blossomforth, you’ve been a big help. I hope you’re feeling better soon.”

“No problem, Twi—er, Princ—um…” Blossomforth blushed, her ears laying back.

Twilight rolled her eyes and smiled. “Twilight. Go on now, and tell the next pony in line to come in, okay?”

Blossomforth returned her smile, and stepped out of the library. A moment later, a black stallion with a silver mohawk entered.

“Hey there, Thunderlane! Why don’t you take a seat, and we’ll get started?”

By evening, Twilight Sparkle was still sitting at her desk, surrounded by the notes she had taken from each pony’s testimony. There had been forty-four pegasi to interview in all, and each had given almost exactly the same answers to her questions. She stared blankly at the fresh scroll in front of her, trying to organize the jumble of thoughts and worries churning in her mind. With a small sigh, Twilight levitated her quill, dipped it, and began to write.

1. All affected pegasi complain of acute exhaustion while flying. Flight time till onset of exhaustion varies per pony.

2. Affected pegasi consistently describe sensation of “heaviness” while flying, and claim this heaviness makes ascending and maintaining altitude difficult.

3. All affected pegasi are, at first glance, perfectly healthy.

4. None of the above symptoms are observed except when the affected pegasi are in flight.

Of 44 pegasi interviewed, 7 have sought medical attention for stated illness. All claim to have been examined and passed with a clean bill of health.

Of 7 pegasi who sought medical attention, all display pronounced symptoms of stated illness. All 7 also noticed symptoms within 3 days of illness’s estimated onset in Ponyville.

Illness seems to have begun in Ponyville early last week (estimated March 5th). Number of affected pegasi has increased steadily since.

Twilight paused, feeling the unease in the back of her mind and trying to form it into a coherent statement. What did she think about all of this? The quill went back to the parchment as she idly wrote down her train of thought.

Symptoms only observed in flight, illness attacks wings? Doctors observed no problems with wings of 7 pegasi... only basic exam though, could’ve missed something. Viral in nature? Spreads quickly, 44 ponies infected in a week, and not all in close contact. Could be carried by earth ponies/unicorns immune to symptoms. No symptoms except when flying, pegasi healthy and strong while grounded... pegasus flight inherently magical... illness possibly blocks pegasus magic?

Twilight stirred from her thoughts and stared at the last line she had written. Illness possibly blocks pegasus magic. In a way, it made sense. All pegasi had an instinctual connection to the magic of Equestria, although they could not channel it consciously like unicorns. Instead, their magic was invoked when they took flight, allowing them to propel themselves at speeds and altitudes far in excess of what their physiology would normally allow.

Her quill scrawled a dark line beneath the final words as Twilight began forming her hypothesis. A disease that attacked the pegasi’s connection to magic... it was an unsettling thought, and Twilight found herself secretly relieved that such a disease hadn’t adapted to affect unicorns. But magic was her specialty, and a disease that worked on a magical level was something she could understand and overcome. With her confidence returning, Twilight continued writing.

Conduct flight tests on infected pegasi, cross-reference data with flight data gathered last year.

Interview doctors who examined pegasi.

Test effectiveness of spells to treat/cure illness.

Determine outbreak’s point of origin.

Leaning back and looking over the finished document and its to-do list, Twilight allowed herself a small smile of satisfaction. She had her work cut out for her, but research in all its forms was a joy to her. She was sure she could gather the knowledge needed to beat this disease.

Twilight rose early the next morning, prepared to throw herself into her project. She began by writing to the Princess, requesting that she compile the reports she had received of the illness; in particular the regions affected, the estimated number of pegasi displaying symptoms, and the approximate date the illness had struck said region. Spike seemed a bit sullen at the fact that Twilight had written the letter herself rather than relying on him to take dictation as she normally did, but he was soon cheered by the promise of a gem snack when she finished the day’s tasks.

Leaving the library, she took flight, wasting no time in seeking out Rainbow Dash again. As she flew, she noticed that she experienced no unusual strain or fatigue. Perhaps alicorns were immune? She spotted Rainbow in the air above a grassy field to the north of town; her favorite practice spot. Twilight approached, seeing that her friend was in full swing, practicing a number of flips, loops and stunts.

“Hey, Dash, do you have a minute?”

Rainbow Dash pulled up out of a high-speed dive. “Oh, hey Twi! You taking my advice and catching some more air?”

Twilight grinned. “I guess I am. Say, Dash, do you think you could do me another favor? It has to do with the pegasi who’ve been feeling sick lately.”

“Sure, whatever you need. Have you found a cure yet?”

“Not quite, but I think I’m making some progress. Do you think you could get some of them together tomorrow for some flight tests? In particular, I’d like to test the ones who’ve called in sick on the weather team.”

Rainbow nodded, folding her arms. “Okay, that makes sense. Where do you want to do the tests?”

Twilight gestured to the field below them. “Here would be fine, if you don’t mind giving up your practice spot for the day.”

“Your wish is my command, Princess,” Dash replied, delivering an exaggerated bow as the two hovered together. Twilight shot her a glare, and Rainbow chuckled.

“I’m kidding, I’m kidding. I’ll let ‘em know to be here. But hey, since you’re up here, you wanna try out some stunts with me? I bet you could pull off some sweet tricks with some practice!” Rainbow did a little loop-de-loop to emphasize her point.

Twilight shook her head, smiling. “I’d love to, but I’ve got a lot on my plate today. Tell the pegasi to be here bright and early tomorrow morning, okay?” Leaving Rainbow Dash with a grin and a wave, she soared off to her next destination: Ponyville General Hospital. Upon entering, she was greeted by a gasp from the receptionist.

“Oh! Oh m-my, Princess Twilight! What brings you here today?”

“Hello,” Twilight replied as she stepped up to the front desk. “Do you know if Doctors Rose and Nightingale are in? I need to speak to them as soon as possible.”

“Oh, dear, you’re not feeling poorly, are you?” the mare asked, wringing her hooves. “I-if it’s not a personal question, your highness…”

Twilight waved a hoof. “Oh, no, not at all. There’s simply a matter of some importance I need to speak to them about. Royal business, I’m sure you understand.”

The receptionist nodded vigorously. “Oh I see, it must be very important! I’ll page them right away, your highness!”

Ponyville’s princess thanked the mare at the desk and trotted off to the waiting room, chuckling quietly to herself. Royalty could be a burden sometimes, but it wasn’t without its advantages.

The interview with the doctors went largely as Twilight had expected; both reiterated the testimony of their patients, and confirmed that all seven of the pegasi who had come to them were, for all intents and purposes, completely healthy. When asked if they had performed anything other than a basic physical, however, both doctors shook their heads. Before departing, Twilight scheduled an appointment for the same seven ponies to receive a more thorough examination, including wing X-rays and blood tests.

Departing the hospital, she struck out for her final destination of the day. As she walked, she mulled over her plans for the flight tests. If she used the data gathered during last year’s Highland Reservoir twister as a baseline, the tests would give her a good snapshot of the rate at which the pegasi’s abilities were falling. And if she could prove that the illness was in some way linked to pegasus flight magic, then she would be one step closer to finding an effective treatment, or perhaps even a cure.

Lost in her musings, Twilight hardly noticed where she was going until she arrived at the ornate doors of Carousel Boutique. Rousing herself from her thoughts, she opened the door, the bell jingling merrily.

“Be with you in just a mi-nute,” a familiar, sing-song voice called from upstairs. A moment later Rarity descended, her head held high as she turned to greet her visitor.

“Welcome to Carousel Boutique, where… Oh my goodness!” Rarity’s eyes went wide when she saw Twilight. “Princess Twilight! You do me such an honor by visiting today!” She performed a graceful curtsey.

Twilight rolled her eyes. “Rarity, I wish you’d just call me Twilight…”

Rarity rose, shaking her head. “But dear, it simply isn’t the done thing! You are a Princess now, proper etiquette must be observed!”

Twilight walked up to her with a small sigh. “Can’t I just be your friend like before?”

“Of course you can, darling,” Rarity replied, grinning and pulling Twilight into a hug. “I was only teasing. You’ll never stop being my friend. I just enjoy being a little dramatic when my humble shop is visited by royalty,” She said, giggling as she pulled away. “Now then, what brought you here today?”

“Well, I was wondering if you had any gemstones to spare. I promised Spike I would give him some for his help with a project I’m working on.”

“Oh, I’m sure I can part with a few measly stones for my precious Spikey-Wikey,” Rarity replied. Twilight followed her into the boutique’s storage room, where Rarity began rummaging through some chests. “Does he have any preference?”

“I think he mentioned wanting emeralds to add to some mint ice cream,” Twilight answered.

“Oh, I have more than enough emeralds to spare,” Rarity said, levitating a sizeable chest down from a shelf and opening it. Bright glints of green danced across her face as the emeralds within caught the light. Raising a large one in her hoof, she studied its facets.

“Mint ice cream, you said? You know, I’ve always wondered how gems taste to dragons. I keep meaning to ask Spike.” She ventured an experimental lick, before smiling and depositing the gem in a velvet pouch. “I suppose it’s just as well I can’t taste them, or I might eat them all before I had a chance to use them in my outfits.” Rarity filled the bag and passed it to Twilight, who stowed it under a wing.

“Thanks, Rarity. How much do I owe you?”

Rarity waved a hoof, frowning as if the offer of payment was an affront. “Oh, Twilight, think nothing of it! I still owe Spike for his assistance in the Boutique last week. Just be sure to give him my love when you give those to him, and we’ll be even!”

Twilight cantered home, the pouch of gems a pleasant weight under her wing. She mentally listed the books and resources she’d need to consult for her research that night. Arriving at the library, she was greeted by the lovely smell of a home-cooked meal. As she stepped inside, Spike called from the kitchen.

“Twilight, is that you? You’re just in time, dinner’s almost ready!”

Twilight quickly stashed the pouch behind an impressively large book (noting the title as Amberbark’s Agricultural Almanac, vol. 19) before heading to the kitchen. Inside she found Spike clad in a frilly apron. He stood on a chair in front of the stove, stirring a simmering pot of carrot and cauliflower stew.

Twilight took a deep whiff of the concoction. “Mmm, that smells delicious, Spike! And good thing, too. I’m gonna need a lot of energy for tonight’s study session!”

“Still working on your secret princess project?” Spike asked as he stirred.

“Yes... I hate having to keep secrets from you, Spike, but...”

Spike tapped the spoon against the edge of the pot. “I told you already, Twilight, it’s okay. Now come on and let’s eat. You need your strength to study, and I need my strength to fetch books and stuff for you!”

Dinner was a short affair of stew and rolls, and after polishing off the meal and washing the dishes, Twilight and Spike were ready to hit the books.

Twilight seated herself at her favorite desk and rattled off the list she had prepared. “Okay, Spike. I need you to find A Guide to Pegasus Anatomy, Pony Plagues and Poxes, and Spells to Soothe the Body and Mind. Also, see if you can dig up the flight data I recorded last year at the Highland Reservoir.”

“On it!” Spike replied with a salute, before rushing off to hunt down the requisite texts. After he had deposited the books and scrolls on Twilight’s desk, she turned to him with a grin.

“Oh, and one last thing... could you grab volume nineteen of Amberbark’s Agricultural Almanac?”

Spike hurried across the room and struggled to shift the ponderous book. It fell to the floor in a cloud of dust, revealing the bulging pouch Twilight had hidden behind it.

“Uh, Twilight, what’s this thing doing here?”

She suppressed a giggle. “I don’t know, Spike. Why don’t you open it and find out?”

Spike undid the pouch’s drawstrings and gasped when he saw what it contained. “EMERALDS!” he shouted, racing across the room to embrace his caretaker. “You remembered! Oh, and they look so delicious...”

Twilight returned the hug, laughing. “They might taste even sweeter if I told you that I got them from Rarity... and that she told me to give you her love when I gave them to you!” Spike’s eyes glassed over as he contemplated the gift from his beloved unicorn.

Twilight giggled once more. “Go enjoy your treat, Spike. I can take care of things for the rest of the night!”

Rainbow Dash came through once again. After sunrise, just after Twilight finished setting up the equipment needed for the tests, a troop of about twenty pegasi began trotting into the field. Among them, Twilight saw the seven who had spoken to the doctors, but as she looked the group over, she noticed that many were ponies she hadn’t even interviewed. Had the disease spread that quickly in a single day?

Twilight began by informing the initial seven of the appointments she had made for their examinations at Ponyville General, promising to pay for them in full (Princess Celestia had granted her a healthy annuity upon her coronation, which could easily cover the costs). Then, after sorting the ponies into groups based on how long they had been suffering symptoms, the tests got underway.

Twilight tested along several parameters: wingpower, top speed, altitude and flight time. As she recorded the pony’s statistics and compared them to last year’s, it became clear that each was drastically underperforming. What was more, it seemed that there was a direct correlation between the time symptoms appeared and their severity. Pegasi who had noticed symptoms within the same time frame all had remarkably similar flight performance. Twilight made a mental note to crunch the numbers that night and determine the average rate of performance loss for each pony.

The tests took nearly the entire day, and the evening sun was casting its gentle light down on the field as the last of the pegasi completed her tests and departed. Twilight was sorting her notes and preparing to pack up her equipment when she spied another mare approaching from town. Recognizing her, she waved.

“Hello, Fluttershy! I haven’t seen you around lately, how have you been?”

Fluttershy approached slowly. “H-hello, Twilight. Um, Rainbow Dash said I could find you out here... she said you were trying to help the pegasi who are having trouble f-flying?”

“That’s right,” Twilight replied, before comprehension dawned on her. “Oh, Fluttershy... you haven’t been having problems flying too, have you?”

Fluttershy stared at the ground, and Twilight could see tears welling in her eyes. “Yes... for a while now... I didn’t want Rainbow Dash or the others to know, so I waited till they were gone. It’s so h-humiliating...” She raised her eyes to meet Twilight’s. “Have you found a way to make it better yet?”

Twilight frowned and shook her head, a pang of sympathy shooting through her heart. “Not yet, I’m sorry. But I’m working on it every day, and if I make a breakthrough, you’ll be the first I tell.” Fluttershy nodded with a sniff, and Twilight rested a hoof over her withers. “Since you’re here, would you like to try the tests? The more data I have, the faster I can find a cure.”

“I’m n-not sure I can, Twilight.” She hung her head, her eyes barely peeking from behind her mane. “It’s been bad for me... worse than the others.”

Twilight rubbed her hoof across Fluttershy’s back. “I tell you what... how about I try casting a spell on you first? I’ve been studying some healing magic, and I think a re-invigoration spell might help the pegasi who are sick. If I do that, will you at least try?”

Fluttershy sniffed once more and nodded. “Okay, Twilight... if you really want me to, I’ll try.”

“‘Atta girl!” Twilight said. Channeling power into her horn, she wove the magic into the formula for the re-invigoration spell. The spell was designed to fill ponies with energy, allowing them to exert themselves beyond their normal limits. Feeling the spell reach full power, she directed it into Fluttershy, a stream of purple light flowing from the tip of her horn into her friend’s chest and infusing her with its glow.

“There we go. How do you feel?”

“A little better,” Fluttershy said. She smiled, throwing her shoulders back and standing a little taller as she felt the energy coursing through her. “Okay, what test should I do first?”

“Let’s start with a simple wingpower test. Just like when you were practicing for the twister last year.” Twilight led Fluttershy over to the starting line, a thin strip of white cloth she had placed on the grass exactly fifty yards from the anemometer. After walking over to the device, she called out to Fluttershy. “Okay, whenever you’re ready!”

Fluttershy crouched at the starting line, flapping her wings rapidly before launching herself forward....

...And hitting the ground again a few feet away.

Twilight’s mouth hung upon. She watched in shock as her friend stood up, staring at her wings. Moving back to the starting line, Fluttershy crouched and warmed up once more, but again failed to take off. She moved back a third time, tears streaming down her cheeks. She flapped her wings furiously and leapt as high as she could, kicking her hooves as if trying to gallop through the air. But her frantic efforts did no more than slow her descent, and she came to a rest less than five yards away from the line. She stood for a moment in silence, trembling, before collapsing to the ground with a ragged sob.

Twilight ran over to embrace Fluttershy, her mind racing. Even the most advanced cases she had tested had been able to fly for upwards of ten minutes before having to land. Was this the final result of the disease?

Kneeling by Fluttershy’s side, Twilight threw her arms around her friend’s neck and draped her wings around her as Fluttershy heaved with sobs. Twilight felt the hot tears seeping into her coat as Fluttershy buried her face in Twilight’s chest. Fluttershy had never been a strong or skilled flyer, and in truth she loved the earth far more than the sky. But for any pegasus to be grounded, completely cut off from the wind and clouds… Twilight couldn’t even imagine the despair the poor pony was feeling.

“I... I could still fly this morning... It wasn’t very far, but I could still fly,” Fluttershy choked out. “Why... why can’t I fly anymore? Why is this happening?”

Twilight had no answers to give. Tears of her own began to spill as she held Fluttershy close. She rocked back and forth, letting the little pegasus ride out her grief.

It was dark by the time Twilight returned to the library, weary and drained. It had taken over an hour to console Fluttershy and walk her back to her cottage. The distraught pegasus had cried until her tears simply ran dry, and when Twilight helped her up, she had followed in a daze, her eyes downcast.

Twilight tossed the sheaf of notes she had gathered from the tests on her desk before sitting, cradling her head in her hooves as she contemplated the day’s events. While they had walked, Twilight had asked Fluttershy how long she had been suffering symptoms. She had mumbled that it had been nearly three weeks.

Nearly three weeks... that would place the time of her infection around the middle of February, much earlier than any of the other ponies. And Twilight’s magic had been completely ineffective... With an exhausted sigh, Twilight undid the twine she had bound her notes in and pulled over a fresh scroll and ink, beginning the calculations of flight efficiency loss for each pony. But it wasn't long before a troubling pattern emerged.

Twilight had expected to find a link between the time symptoms started and their severity; what she hadn't expected to find was that the ponies’ flight performance was dropping at a precise, fixed rate each day. Each pegasus’ flight stats were dropping steadily, and when she factored in time of infection and extrapolated from last year’s stats, she arrived at an exact 5.7% drop in wingpower per day, per pony.

She stared at the figure. If this were a disease, the progression of symptoms ought to fluctuate between ponies, depending on the strength or weakness of their immune systems.

The door opened and Spike entered carrying an armful of scrolls, pulling Twilight from her reverie. “Oh, hey, Twilight, you’re back! How’d the tests go?”

Twilight gave her assistant a thin smile. “They... went well,” she replied, trying to drive the memory of Fluttershy’s breakdown from her mind.

“Good. Oh, did you find the letter from the Princess? It came while you were gone, I left it on your bed.”

Twilight stood from her desk and trotted to her room. Sure enough, a scroll with a familiar seal rested on the pillow. Unrolling it, a spark of hope flared within her. It was the compiled reports she had requested from the Princess. But her heart fell again as she paged through it and came across a map of Equestria.

Every major city and region across Equestria was marked in red, with an annotation by each declaring how many pegasi had been infected, and the dates on which reports from that area had been received. Even Cloudsdale was not exempt, with a full twenty-six percent of the pegasus bastion’s population displaying symptoms.

More worrying, however, were the dates. For each region, the majority of the infected pegasi had begun suffering the illness on or after March 6th, much like Ponyville. But the first reports for each city placed the initial date of infections much earlier, sometime around February 18th. Almost exactly when Fluttershy’s symptoms had started.

Twilight stared blankly at the map, her mind racing. There was no way a plague could have spread this quickly. For each region of Equestria, a land thousands of miles across, to be infected almost simultaneously...

Once more, Twilight’s thoughts were interrupted by Spike, stepping into her room to speak.

“Oh, one more thing, Twilight. Doctor Rose came by while you were gone, and she asked me to tell you that she examined the pegasus ponies like you asked. She said the X-rays and blood tests all came back clean.”

My Dear Princess Celestia,

I write to you to report the initial findings of the research I have conducted on the pegasi of Ponyville. While I am afraid I have made little progress in the days since you requested my assistance, I feel that what little I have learned is of great enough importance to be worth informing you.

I have been operating under the hypothesis that the illness in question works on a magical level, effectively limiting (or, in extreme cases, entirely blocking) the magical elements of pegasus flight. I came to this conclusion after observing that of all the pegasi studied, each was seemingly in perfect physical health. This was further confirmed by professional medical diagnosis (see p. 5 for statements by Doctors Rose and Nightingale).

This illness behaves very strangely, apparently affecting clusters of pegasi each day, and continually sapping their flight abilities at a fixed rate per day thereafter (see p. 6). It is my belief — and fear — that the ultimate result of this progression will always be the same: rendering the pegasi completely flightless.

Lastly, I wish to direct your attention to the blood test results (p. 7) of several affected pegasi, as well as the map included in your compiled report (p. 15). As you can see, each pegasus examined was completely free of any anomalous bacterial or viral agents, and as the map illustrates, each region of our land, separated by hundreds of miles, was affected almost simultaneously.

With these two pieces of information in mind, the only conclusion I can draw is that the illness is not in any way pathological in nature. No disease is capable of spreading so quickly, or evading all forms of detection. I can further attest that the malady is thus far impervious to magic, having stymied every healing spell attempted.

It is with sadness that I must confess that this illness has eluded my abilities as a researcher. I have no idea where it came from, how it works, or even how it may be treated, let alone cured. If I were a superstitious mare, I might call it a curse... but until I learn more, I am afraid I will be no closer to a solution than when I began.

Regretfully,

Princess Twilight Sparkle

Stone-faced, Twilight set her quill down and rolled the letter up with copies of the relevant documents. Hoofing them to Spike, she watched impassively as he sent them off, the flash of green flame reflecting in her half-lidded eyes.

A week of hard research... and for what? What did she have to show for it, aside from vague guesses and anxiety? What had she learned, except that her friend may never fly again? An image of a sobbing yellow pegasus, trembling in grief and shame, flashed across Twilight’s mind, and she sighed. She had failed.

She looked across the expanse of her desk, piled high with notes, reports, statistics, interviews... information completely wasted, because it had not brought about progress. She might as well have been doodling like a little filly, for all the good she had done.

After an hour of brooding, Twilight received Celestia’s reply.

My Dear Princess Twilight,

When I wrote to you and requested your assistance in this matter, I did so in the hope that your findings would quell the unease which has been growing in my heart of late. The issue of this illness has weighed heavily on me, for I had my suspicions of it’s cause before I enlisted your aid. Rather than assuaging my fears, however, I am afraid your discoveries have only confirmed them.

I feel you are right in your assessments thus far. The malady in question does indeed affect the pegasi's magic, and is not transmitted from pony to pony as a virus or bacteria is. Rather, it is a much deeper problem, and I dread that it may not end with the pegasi.

I must again ask, my protege, that you let nopony else see this letter... indeed, it may be best to burn it, for what I am about to reveal to you could cause a mass panic were it made known to the public.

The reason behind this illness, Twilight, is that magic in Equestria is dying.

A sharp knock sounded on the library’s front door, and Twilight jumped, gasping. After scrambling to stash the letter amidst her research documents, she answered in a shaky voice.

“Y-yes? Come in!”

The door opened, revealing Rainbow Dash. She stepped inside, a sheepish grin plastered across her face. “Hey, Twi. You’re not busy, are you?”

Twilight put on a false smile, the Princess’s words still emblazoned in her mind. “No, not at all. What do you need?”

“Well, uh, you know that bug that’s been going around? The one that makes it hard to fly? You’re still working on a cure for that, right?” Rainbow asked, licking her lips and rubbing the back of her head.

“Yes,” Twilight gulped, a chill running down her spine. “Why... why do you ask?”

Rainbow shuffled her hooves, chuckling. “Well, heh, y’see... this is a little embarrassing, but... I think I may be coming down with it, too.”

Princess Celestia stood on the balcony outside her bedchamber, gazing into the horizon. Her face was placid, giving no hint of the turmoil within her. The evening sun hung low, its lower rim just grazing the horizon as Celestia completed her duty for the day. Behind her, hoofsteps approached.

“Good evening, Luna,” Celestia said without turning.

“Good evening. Have you informed Twilight Sparkle of the situation?”

Celestia nodded, her eyes closed. “Yes. I can only hope she will understand. Our world is changing... I fear irrevocably. She has a hard road ahead of her.”

Luna nuzzled Celestia’s neck. “I believe she has the strength of spirit to walk that road. You chose well when you made her your apprentice.”

“I hope so, sister, for the sake of all our subjects—”

Celestia stopped short as she felt a deep rumbling. For a brief moment, she thought the turmoil in her heart had translated itself into her body. But the shock in Luna’s eyes and the rattling of her bedchamber’s windows told her otherwise.

As swiftly as the tremor began, it subsided. Beneath the balcony, guards ran about amidst the barking of orders. Luna turned to her sister, her breath coming short as she spoke.

“Celestia, what was that? Is it over?”

Celestia returned Luna’s gaze.

“I only wish it was.”