Tick. Tock. Tick. Tock.
Time was running short. There was a certain margin of error, of course, when it came to the schedule—there always was, when working with unreliable agents in the mix. That fact, however, did nothing to soothe Antenna's nerves. After all, what changeling wouldn't be afraid of Her?
Five minutes. Only five more minutes before the risk would outweigh the benefits. Antenna paced back and forth, heedless of the occasional stares thrown her way by other ponies. This was an important mission—no, a crucial one—and the best they could do was rely on luck? It was infuriating. It was miserable. It was an indignity that no proper changeling would stand for.
And yet, here they were. Thanks to Chrysalis.
Antenna didn't really like Chrysalis. She was a fine leader—no, a good one—but... She was rash. She was impatient. Her transformations were par none, but she had not the eye for detail. She wasn't good at deep infiltration, and she knew it—but she had pushed forward with her plan anyway.
Four minutes. Antenna stopped pacing to look around. Everything seemed fine still. Thunderlane buying flowers from a stall. A couple walking by, lost in each other's eyes. Lyra with her instrument, reclining on a bench. Nothing suspicious. No guards, in disguise or out. No magic lasers flying her way. And, most importantly, no mailmare that was supposed to be here ten minutes ago.
The plan in itself hadn’t been bad. However, the details of it certainly were. In particular, the fact that Chrysalis would be the one to take Cadance's place. Everyling had known it was not a good idea, but none dared voice the sentiment. They knew, and Chrysalis did too. That she had made it a part of the plan anyway, spoke volumes of her position on the matter.
Antenna was not surprised when the plan had failed. No, indeed, she had been half-expecting it. Thankfully, her job in Canterlot had been done weeks before the invasion, and as one of the best infiltrators, it was decided by the hive to keep her away, and hidden.
Three minutes. She started pacing once again.
The Canterlot fiasco by itself had been bad enough, certainly. Not only were many an established disguise burned—and even more changelings lost—now the ponies had a certainty of changeling's continued existence, they knew what to look out for. Changelings were being discovered one by one, singled out flawlessly by Her creation.
A spell, one so simple a foal could learn it, that could see through a changeling's lie, exploiting weaknesses in their disguise magic that they themselves knew not of.
Two minutes. Antenna surveyed her surroundings, making sure her path of retreat was still clear. She intended to wait out the window of time that she had to the last second, but that didn't mean she was going to be sloppy about it. She adjusted her tinkling saddlebags—full of all kinds of alchemical produce—and fluttered her wings to make sure she could fly at a moment’s notice.
She didn't need to check the watch hanging from her neck to know how much time she had left—she could hear it ticking, counting seconds down, but she lightly tugged at it nonetheless, playing with it with her hoof for a couple of seconds.
Indeed, their situation was dire, but it was surmountable as well. Changelings might not be the best at combat, but they were passable—certainly better than the average pony. More importantly, they knew how to run. They knew very well how to run away, and no one short of a professional would be able to catch a changeling on the run in any meaningful way.
More than that, they could always withdraw from Equestria altogether. It would be a terrible blow, one that would take decades to recover from, but it was preferable to extinction or capture. With time, they would be able to work out those imperfections that Her spellwork abused, and then they would be free to roam Equestria once more.
Provided She didn't create something worse.
A minute left. Antenna was now standing near the alley that she was going to retreat through. She scoffed. While she was hesitant to use the pre-planned path—seeing how close she was cutting it now—there wasn't really any space for improvisation, short of flying away at full speed.
No, everything up until recently wasn't a grave problem. That changed, however, about a week ago. That was the first time a changeling had gone missing. Not killed, no—his presence could still be felt in the hivemind. And not captured—all attempts at communication failed.
Missing. There, but also not. Within a thought's reach, yet inaccessible.
Ponies could've managed to block the connection, proposed one.
Impossible, chorused the Hive.
It was indeed impossible—but so was thought a spell which could reveal changelings.
A deserter, ventured another.
Impossible, chorused the Hive once again.
While indeed they were individuals—not a single organism, but rather many separate parts of a greater whole—it was practically impossible to hide something like a betrayal.
No more opinions were forthcoming. The Hive was stuck, torn between two unthinkable options.
Then, a second changeling went missing. The hivemind nearly upended itself in agitation. In the end, the Queen had to step in and bring everyone to order, having come out of her funk for the first time in weeks.
Chrysalis' proposal was reasonable—simple, and effective, and ruthless. It was not a certainty, but the Queen did not parade it as one—something that, evidently, won back a lot of respect—and it was the most practical option offered yet.
Sacrifice a single changeling—someone frail, and old, but unwaveringly loyal—send them to Ponyville in disguise, to be caught by Her. A simple thesis—if it is a spell, then she would be cut off the moment she's found out, and if the two lings truly deserted, then the communication will be maintained.
Nonetheless, despite the practicality, it warranted discussion—until a volunteer came forth. It was decided then.
The plan had been modified just before being carried out, however. New information had been acquired. The missing changelings were sighted in Canterlot, departing for Ponyville via the train.
They were being escorted, but none of their magic was restricted. The evidence was inconclusive—it was decided to carry on with the infiltration. However, it was no longer a simple binary test. The infiltrator will attempt to contact the other two, and find out more information from them.
Then, if possible and needed, she will commit it to paper and try to find a way to post it, to a specific place, at a specific time, and to a specific pony. Not impossible with pony postal service, but certainly questionable in light of being a changeling.
Worst-case scenario, they still got the simple result, and would now know which of the two impossibilities they it was. Best-case scenario, they may just receive some valuable information.
"..llo? Hello, miss? Do you hear me?" Antenna was jarred from her musings by a grey pegasus mare. She was wearing a mailmare's uniform, and had a fitting pair of saddlebags slung over her back.
"Uh-huh," muttered Antenna, then shook her head, "Sorry, I mean, yes, yes I can. You are the local mailmare, correct?" Her time had basically run out, she needed to hurry the conversation along.
"And you are..." she paused for a moment to focus her eyes on the envelope she pulled out of her saddlebags, "miss Quick Delivery, I presume?" At a nod from Antenna, she sighed tiredly, "Sorry for the delay, I got held up with another package. Anyway, please sign here, and here, and thank you. Here's your letter."
"Thank you," Antenna nodded, taking the letter and safely stowing it away in her own saddlebags. Now then, she moved to speak before the other pony could leave, "Ah, sorry, but before you go, the waiting has left me a little peckish, so if you could possibly point me towards some cafe nearby..?"
"Errm…" she had to pause for a second, "there is one not far from here, just through this alley actually, then a turn left, and a turn right, and you'll be right there."
Antenna had to stop her face from morphing into a frown, "Thank you."
The mailmare nodded once, “You’re welcome!” and flew off, swaying slightly. Now that she was gone, Antenna let her scowl show for a moment, before shaking her head to recenter herself. Afterwards, she quickly turned around and made her way into the alley.
Alright, Tenna, now’s the simple part—just get out of town, no problem, right? She was running almost two minutes late.
A unicorn stallion came out the other end, patting down his mane. He trotted with a purpose, turning right to walk down the street. He didn't look too much in a hurry—a smile on his face, humming a simple tune to himself. It was a nice day out, sun shining down on Ponyville with nary a cloud in sight.
At the intersection, he turned left, a cafe now in his sights. It was mostly empty—only a few ponies sitting around—so he walked in confidently, sitting down at one of the tables closer to the bathrooms, and waited for a server to come by.
The stallion started tapping a hoof on the table impatiently after a minute. The cafe wasn't particularly busy, and that made the delay all the more frustrating. Finally, a staff approached him.
"Good day. Would you like a menu?" A petite earth pony, small polite smile on her face.
"No, thank you. I would just like a coffee, and a pair of eclairs," the stallion paused momentarily, then smiled just barely, "chef's special."
The mare nodded, "as you wish," and promptly left with the order.
The stallion sighed contentedly. Then, he pulled out a newspaper from his saddlebags and started reading it. After a couple of minutes, he put it down on the table to mark it occupied, and went into the bathroom.
Antenna shed the disguise the moment she was inside the bathroom, door closed behind her. She made sure there was no one inside while she waited out there, and so felt safe in showing her true form.
The next transformation was going to be problematic—even for someone as experienced and skilled as her—and being in the natural form helped with transformations immensely.
She focused inwards, starting the transformation from the inside, first changing and compressing her innards, and then moving onto her carapace. Once finished, a flash of green fire washed over her, she now looking for all the world like a small kitten.
Antenna purred in delight. It has been a while since she last did a transformation as drastic as this—she practised before the mission, of course, but it just wasn't the same as doing it in the field—and it wouldn't be an exaggeration to say that this escapade's success hinged on her being able to do it.
While Her spell truly was terrifying, it was thankfully not without a fault, either. They had figured out a couple of things over the month, through trial and error, and reasoning.
Its effects could be detected by none—bar the Queen herself—sure, but it took some time for the spell to complete its work. In addition, changing one's disguise seemed to prolong the time required—and the more extensive the changes, the greater the effect.
Thus, any changeling that had a reason to suspect danger, could make a reasonably good escape despite the spell, even if it resulted in burning the particular disguise that had come under scrutiny.
She quickly found the hole prepared for her, and jumped through it in one fluid motion. On the other side, the mare from before was waiting for her.
"Awww, you poor little thing, are you hungry again? Here, how about I give you a bit of milk, would that be alright?" She continued on and on as she carried Antenna through the kitchens and towards the backdoor.
Somewhere along the way, she picked up a small piala filled with milk. Looking around, Antenna could see that no pony spared them so much as a second glance, apparently used to seeing something like this often enough, and they made it out without trouble.
Once they were outside, the pony sat her down, looked around, and discreetly dumped the milk in a nearby bush, "There, now do run along my dear, I'm sure your mommy can't wait for you to come back," she near-whispered to the kitten, then turned around and went back inside.
Antenna quickly stretched her limbs, and set off at a brisk pace towards the edge of town, where the train station was situated. The street along which she traveled was rather crowded—seeing as a train just arrived recently—and so she had to concentrate on weaving through the forest of legs that surrounded her.
Nonetheless, as she saw the train station come into view, she let herself relax just a little. She was almost out. On the train, it would be a piece of cake to transform into some manner of bird after secluding herself in a bathroom, and then fly out of the window once it was far enough from Ponyville.
Even if her disguise were to fall apart, as long as she was alone, she could just reapply it on the spot. She sharply turned left, ducking into an alleyway between the train station and a pair of houses. There, in a hidden spot between the houses and away from prying eyes, she slowly transformed into a burly earth pony mare.
Success was within reach, Antenna knew, but dared not tempt fate with premature celebrations—if her decades of life experience had taught her anything, it was that fate could be a very cruel mistress indeed.
So lost was Antenna in her musings as she walked, that she was unable to react in time to someone suddenly stepping around the corner, the two of them both stumbling back from the impact.
Antenna shook her head, but before she could recenter herself and look at the other pony, she heard the stranger speak.
"Ah, finally," slowly, rigidly, the changeling raised her head to look, "Hello there, Antenna. It is such a pleasure to have met you at last."
Author's Note
Well, this was a blast to write! Not entirely satisfied with it, to be perfectly honest, and had some good feedback that I was unable to implement, but whatever.
Thanks to Mitch, Zontan, Flash, and Winternacht for giving it a quick pass 
