Three days have passed since the Royal Wedding in Canterlot, and the time has finally come for the six friends from Ponyville to make their way home. They leave the palace in the early afternoon, accompanied by Princess Celestia, who has insisted on escorting them as far as the train station.
She walks near the front of the group, speaking with Twilight, whilst the rest follow close, smiling and sharing anecdotes of the hectic past few days. But unbeknownst to the others, one of their number lags behind with an uncharacteristic frown on her face...
Pinkie Pie narrows her eyes at the back of Applejack's head, as the farmpony tries and fails to hide her giggling along with Rainbow Dash. Fluttershy and Rarity are off to one side, talking about dresses or some such, so they don't notice. Nor do Twilight and the princess. But Pinkie Pie does.
It seems that every time those two are alone together, even for a second, they start talking in hushed voices and laughing at private little jokes. Pinkie wasn't born yesterday – she knows there's obviously something going on between them – but she doesn't care about that.
...Well, maybe she cares just a little bit. But that's not important. The thing that's really bothering her is that she's feeling left out...
“Are you alright, my dear?” comes a voice from beside Pinkie.
She turns and sees Princess Celestia standing beside her, with a questioning smile on her face. Twilight has been left at the front of the group, but she doesn't seem to mind, except that she casts a couple of funny glances over her shoulder every now and then.
For her part, Pinkie lets out a grumpy 'harrumph'. “Dashie and Applejack have been sneaking around and laughing all day,” she explains. “But whenever I ask what they're laughing at, they say it's nothing.”
She hardens her glare on the back of Applejack's hat. “...Inside jokes are no fun.”
“I see,” says the princess calmly. “I enjoy the occasional joke myself, but I certainly agree that they are more fun when shared with friends.”
Pinkie Pie nods at the wise words. There is a pause, during which she continues to stare at the offending farmpony. All this talk of inside jokes gets the parts of her mind that aren't busy glaring to start thinking, and she recalls something from the wedding. Her ears perk up with interest as she turns to the princess.
“Hey, in that case, can I ask you something?”
The princess tilts her head and smiles expectantly.
“How come you laughed when Princess Luna asked whether she'd missed anything?”
Celestia blinks. “I beg your pardon, dear?”
Pinkie rolls her eyes. “You know, after the wedding, when Shining Armour and Cadance started dancing. Princess Luna appeared out of nowhere and said 'Did I miss anything?' You laughed, and so did she.”
“You... cannot possibly have heard that,” Celestia says, and her smile falters a little. She almost sounds surprised.
“Duh, I can hear even the teeniest laugh from a mile away!” Pinkie informs her. “So c'mon, tell me the joke!”
Celestia has slowed down a little now. Her smile has been replaced by an unreadable frown, and she's looking ahead, instead of at Pinkie. “...Why should it not be simply because my sister was being ironic?” she asks.
Pinkie shook her head. “Nope. I thought about that. It wasn't that kind of laugh. It was that kind of laugh--” She points at Applejack, who is shaking as if laughing, though no sound is coming out. At her side, Rainbow Dash is smirking and fluttering her wings proudly.
There is another silence. Pinkie looks expectantly up at the princess, whilst Celestia stares, in thought, at Applejack and Rainbow. After a long moment, Celestia lets out a sigh through her nose.
“It is clear that there is no fooling you, Pinkie Pie. I assure you, it is not my intention to deceive--”
“Great! Then tell me the joke!”
“It is not a joke, in the way that you think of them,” says the princess sternly. “We laughed, certainly, but it was not out of humour. More of understanding, and relief...” She breathes a quiet huff. “If you wish for answers, then I will grant them. You have earned that much. But I can promise that you will not find such answers to your amusement.”
Pinkie hesitates. That there is no joke to be had is a little disheartening, but she finds herself becoming more curious now. If not a joke, then what was Celestia laughing at?
Refocusing, Pinkie bounces in the air and resumes her smile. “Okie dokie lokie! I wish for answers!”
“...Very well,” says Celestia. She pauses for a moment, as if deciding where to begin, then closes her eyes. “Did you think it at all odd that my sister was absent during the entire changeling attack? That she only appeared at the very end, after the danger was gone?”
Pinkie curls her lip. “Kind of, but I just thought she was sleeping. Or maybe that she got locked in the bathroom.”
“Locked in the bathroom...” Celestia repeats thoughtfully. Her smile returns to her, and she gives a little chuckle. “Yes, I suppose that is an appropriate metaphor.”
The princess pauses to look up at the Sun, still high in the sky. “I have ruled over Equestria for more than millennium now,” she says. “Ponies do not simply rely on me for advice and guidance, as they once did. A structure has been established. I preside over disputes, I am an ambassador to other races, I make decisions affecting the entire land every day.
“...What do you suppose would happen if I were to suddenly disappear?”
Pinkie quirks a brow. “Disappear? Like, go invisible?”
Celestia shakes her head and smiles. “When Queen Chrysalis revealed herself, for example. You saw how she overpowered me with her magic. If she had not stopped when she did, I could easily have been lost in that battle.”
“Oh, I get it!” says Pinkie happily. “You don't have to worry about that, we'd find you. Promise!”
Celestia doesn't laugh, she just gives Pinkie a sidelong look. “...And if you could not? If I was lost to you forever?”
Pinkie's smile falls as she racks her brain for the answer. “Then... you'd win at hide and seek?” she guesses.
“The structure would collapse,” says Celestia darkly. “Relations would become unsteady, confusion and panic would spread. There would be chaos, perhaps even enough to unleash Discord again. If that were to happen, not even the Elements of Harmony would be enough to keep Equestria from falling into darkness.”
Pinkie's ear twitches nervously. “Well, that's not very optimistic,” she mutters.
“It is a realistic scenario,” says the princess. “I have no doubt that, in time, ponies would find a new ruler, or a new system of government entirely, so that they would be able to thrive without me. But Discord's release would make that all but impossible. That is why Luna was absent from the attack.”
At this point, Pinkie furrows her brow and looks down at the pavement. Even she has trouble making the connection between Luna's absence and Discord.
Luckily for her, the princess notices her confusion, and explains. “Shortly before I sent your invitations to the wedding, I sensed a great and imminent threat to Canterlot. I made many preparations – Shining Armour's shield and the increase in guard, to name a couple – but in the end I had no idea what we were about to face.
“Then, the night before the wedding ceremony itself, the sense of danger grew much stronger. I knew it was close, but still there was nothing more I could do. Except for one thing...”
“Princess Luna?” Pinkie guesses.
Celestia nods.
After giving it a moment's thought, Pinkie gasps in realisation. “You locked her in the bathroom?”
“So to speak,” says Celestia. “I sent her away from Canterlot, so that she would not be here when the danger arrived.”
“But why? Didn't you think she could've helped?” says Pinkie. “I mean, if she was there, you two might've been able to beat Chrysalis all by yourselves!”
Celestia inclines her head. “Might being the operative word. I had no way to know that we would overcome the threat, nor that either of us would emerge from it unscathed. I sent Luna away to make sure that she was safe...”
She pauses and smiles beside herself. “...She is stubborn, my sister, and we argued for much of the night. Ultimately, she submitted... albeit reluctantly, and only after I explained that my decision was not made for her safety, but for that of Equestria.
Pinkie Pie blinks dumbly. Despite the look on her face, the pieces are starting to fall together. The safety of Equestria, the 'structure'... it all makes sense now that she thinks about it. The excitement makes her ears perk up again.
“I get it! Equestria needs somepony to look after it, otherwise Discord gets out and all the rain turns to chocolate. And looking after Equestria is your job, but Princess Luna used to do it too, so if you were poorly or something, she could probably take over for a bit. So when you thought there was trouble coming, you sent Princess Luna away so that she could take over when you--”
Pinkie breaks off, and her ears begin to droop sadly as she understands. She's not sure that she wants to finish the explanation, but even if she doesn't, she'll still know. Her frown deepens as she concedes and mutters...
“...When you got lost forever.”
Celestia isn't looking at Pinkie. Pinkie isn't looking at Celestia.
It's hard to think of anything else to say, and that feeling is both uncommon and unpleasant to Pinkie Pie. She understands serious things. Ponies never believe her when she says so, but she really does. She understands sacrifice – giving up something special or fun to you, in order to make somepony else happy.
That the princess is willing to sacrifice herself for Equestria is noble and brave and selfless... But that she has actually thought about it – planned it – is just... wrong.
“That's wrong,” Pinkie says aloud.
Celestia looks at her sidelong, while Pinkie turns to give her a full-blown frown.
“You're not supposed to think like that. It's p-- per-- press--” She screws up her eyes and tries to focus. This is important. “It's pessimistic!” she finishes.
“It's realistic,” says Celestia. “And it is my duty as a ruler to think as such.”
Pinkie shakes her head violently and plants her hooves on the pavement, coming to an abrupt stop. “No, that's wrong!”
A silence seems to fall over the entire street. The group stops, and every one of them turns to Pinkie with shocked or quizzical eyes. A few passers-by stare at her with interest and awe, whilst the guardsponies – who had been escorting them from a respectful distance – begin to look uneasy.
“P-Pinkie Pie?” breathes Twilight, eyes wide and jaw slack as she glances between Pinkie and the princess.
Under everypony's gaze – including Dashie's – Pinkie begins to realise how she must look, glaring at the princess and being all shouty. She hadn't meant to get all grumpy, but--
“It's alright, Twilight,” says the princess calmly, waving a gentle hoof and offering her a smile. “That was my fault – I said something that I should not have...”
Twilight creases her brow and works her jaw for a moment, before closing her mouth and throwing a questioning look at the others.
Celestia turns back to Pinkie and bows her head. “Please, forgive me, I did not mean to upset you.”
“I... No, you--” Pinkie begins, though she is cut off by a stern look from Dashie. The pegasus with the tasty rainbow mane shakes her head, like she always does when she's trying to stop Pinkie from saying something dumb.
Pinkie stares at her for a moment, before frowning deeply and hanging her head. “Okie dokie, princess...” she mumbles. “I'm sorry too.”
“That is quite alright,” says Celestia. She offers a faint smile.
An uncomfortable silence falls over the group again. Pinkie Pie continues to look down at the ground. Nopony moves.
“Oh! Look where we are!” says Twilight, in a loud and deliberate voice. “The train station is right around that corner, ha ha!”
Celestia grunts and looks around, then she chuckles. “So it is. I suppose that we should part ways here then. If you hurry, you may just catch the next train.”
“Yes! Of course, princess!” says Twilight brightly. “Thank you for walking us here! We'll send you a letter when we get home. Come on girls!”
Looking up, Pinkie receives a deliberately toothy smile from Twilight. It makes her feel a bit better, and the little boost is enough to get her up and trotting forwards.
“Pinkie Pie,” says Celestia, after only a few steps.
Pinkie turns around to see a small smile on the princess' lips.
“I trust that our... 'conversation' will stay between us,” Celestia says. “I would not want it to upset anypony else. Especially Twilight...”
Pinkie opens her mouth and hesitates, another experience that is rather uncommon to her. She would never want to upset anypony, of course... but, for some reason, it isn't so easy to just say 'Okie dokie lokie' to this one. Something here is decidedly wrong, and she can't just keep quiet about it, can she?
“Pinkie Pie, come on! The train will be here any second!” Twilight calls from around the corner.
The princess and the party pony stare at one another for a long moment. Ultimately, Pinkie is forced to resign to the fact that there is nothing she can do right now. A problem like this is going to take a lot of time, planning, and possibly partying, to solve.
She gives Celestia a slow and measured nod, but deliberately avoids a Pinkie Promise.
Then she blinks, breaks out a smile, and skips after her friends.
Author's Note
So, this was intended to be a one-shot, but I left the ending open because I can see how I could take this in a further shipping/friendshipping direction. ~~For now, it's marked as complete and should considered a snippet, but I'll be putting some thought into continuing it.~~
~~I've now decided that I~~ will ~~continue this at some point, thus the tag change to 'On Hiatus'. I've still got a~~ LOT ~~to do beforehand - so don't expect it any time soon - but you can rest assured that it will be done.~~
It's been aaages since I wrote this and I've only just realised it's still 'on hiatus'. I'll have to go back on my original word unfortunately, and say that this is not going to be continued. Any ideas or inspiration I did have for it are plain gone by now. Sorry on the off chance that anyone was waiting for this to be continued 
Thanks for reading, I hope you enjoyed it!
