Stress levels were already high, with Twilight directing her first royal Hearth's Warming pageant and unexpected snowstorms escaping the Everfree. Then the changeling army arrived.
Now, with Queen Chrysalis holding Ponyville hostage and the clock ticking on suspiciously pointless negotiations, it's up to Rarity to match wits with the invaders and save the holiday. However, as she digs ever deeper into the queen's tangled plot, what she learns could force her to choose between her friendships and her conscience.
Off-season note: This is a Hearth's Warming story like Die Hard is a Christmas movie (but with espionage instead of explosions). Don't skip it just because the holiday's over. 
Critical praise:
"A high-tension thriller where nothing is what it seems." — Titanium Dragon (rating: "Highly Recommended")
"An entertaining ride from start to finish … watching all the pieces fall into place is fantastic." — Present Perfect (rating: "Highly Recommended")
"Props to horizon for an intricate web of deception. Most writers have difficulty with crafting mysteries … this one, however, had me completely fooled from beginning to end." — PaulAsaran (rating: "Why Haven't You Read This Yet?")
"It’s a rare mystery and thriller that can keep things tense and make the mystery actually tough to guess as you go along, while still feeling like a natural conclusion. ... The end result of layers unveiled and red herrings contradicted makes it sing." — Ghost Mike (rating: "Really Good")
Second-place winner in the "Behind Closed Doors" December writeoff, now expanded and revised! Featured on EqD! Rated "Recommended" by MLPmatthewl419!
Big thanks to Titanium Dragon for post-Writeoff editing assistance.
Comments contain spoilers!
Well, color me intrigued. This one looks neat.
AND OF COURSE I AM ALWAYS A FAN OF CHRYSALIS AND CHANGELINGBOAT-DIPLOMACY.
Main thing I'm kind of curious about, though, is why you decided to go for a first-person perspective on this one. It's not really clear that it's Rarity's perspective we're following until maybe a dozen lines in, and while the story seems to have a vague Rarity focus, it doesn't seem like her perspective has all that much to add to everything going on around her. Is this something you're planning to bear out in future chapters, or is this some kind of narrative artifact from an earlier planning stage? So far it seems like you could've done everything pretty easily in third person omniscient.
Hearth's Warming Eve? More like Hearth's Swar... oh.
um. Carry on.
WARNING: COMMENTS ON LATER CHAPTERS CONTAIN MAJOR SPOILERS
(If you're checking comments to see what other readers thought of the story, I've linked several detailed spoiler-free reviews in the story description.)
5418262
Thank you! I shall endeavour to fulfill your intrigue needs (especially the ones you didn't know you needed).
Without spoiling anything for the non-Writeoff audience, this chapter is the backswing of the cartoonishly large Rarity warhammer.
5418263
5418283
Chessmaster Rarity is bestmaster Rarity, so I personally highly await this.
Oh! I get it! I get it! XD
Hell hath no fury like a marshmallow scorned.
This looks fun
5418262
The story is written in first person Rarity perspective mainly to give the narrator the opportunity to comment on the actions of others from Rarity's point of view.
5418344
mylittlefacewhen.com/media/f/rsz/mlfw47_small.jpg
You get all of it?! Madness!
... though given your track record on Hard Reset 2, maybe I shouldn't be surprised.
Oh dear, this appears to be terribly interesting. I am afraid I shall have to track it. Terribly sorry. May even have to upvote it, as it seems awful good right off the bat.
5418737 Indeed. The only thing that doesn't quite fit is this marginally un-Rarity-like line:
5419659
Terribly tragic, to be sure.
I liked this story when you had to make it fit inside eight thousand words. I'm sure I'm going to love the full version. I look forward to it.
5419065 Okay question... didn't Chrysalis ask for everyone to come at the negotiations? Also... you think she'd have better intel. Not having intel is stupid of her especially for a race of infltrators. This is a flimsy thing really... too flimsy to be honest.
5421302
Thanks for reading and commenting!
Yes, it does seem odd that Chrysalis doesn't have better intel, doesn't it? As Rarity herself comments:
There's definitely something strange going on there, isn't there?
Perhaps today's chapter will explain … or maybe it'll just deepen the mystery for tomorrow.
5419804
Good point - not sure how that one got through my edit passes. Ninja-improved!
5422181 maybe i shall read n say.
Wait, what?
What?! 
UPDATE NOW!
WHAT A
!
So has Rarity been a changeling the whole time? So many questions! Curse you for waiting to publish the last chapter! Curse you!!!!
5422476 or wait, double twist! What if Rarity is disguising herself as a changeling? What if that's not queen chrysalis? What if thats a windigo?!?!?
5422489
Actually, every single character is a changeling -- except for Chrysalis, who is actually Princess Luna with a mask on.
... Maybe I should have spoiler-texted that.
5422821 Holy shit rarity is suffering from immersion!!!
Also wait what? At both me and you.
5419065
Oh no, I meant, I get the title. ^^
Awesome so far. This Rarity reminds me a lot of the Rarity from Friendship is Dragons.
Now this looks like a hell of a lot of fun.
All of my yes.
Well, this is certainly a change. Should be interesting seeing how this adjustment ripples through the rest of the story
Also, I really like the ambiguity of that second-to-last line. I can think of three different interpretations of it off the top of my head.
Well that's a suspicious bit of internal dialogue for Rarity right after she looks into her pocket mirror.
Hahaha!
Whisper Song is twelve? Wild guess time, the entire army is made up of changeling children because that's all Chrysalis has to work with after the failed invasion.
Go Fluttershy!
Wait, what? Hmmnn.
5423471
As I said in the writeoff thread, because of the wordcount derail, I never originally got to write the climactic scene that the entire story was building toward.
I look forward to actually resolving the mirror plotline this time.
Aww... where's the ending? It's Dec. 25th...
5425202
I was just helping him edit it; it is very nearly done. It should be out soon.
5425241
11th hour lol
You're welcome, Horizon! I was glad to have helped out with this story, as I am rather fond of it.
Plus it meant I got to read it before all the plebians.
I definitely like the new ending better than the old one.
5425570
But it's posted and it's not midnight yet!
More like 15th.
YESYES YESYESYES!
EDIT: now that I've actually read this final chapter, thank you :) thanks for giving me a Christmas treat to read, with wonderful subterfuge and Fashion Pone being best horse. And for sticking up for me regarding Babscon. Youre a cool dude Horizon.
Now get that other damned changeling fic out!
Even better than the shorter version.
I think the only thing I feel uncomfortable about is the ponies (Mane 6 in particular) reaction to the fate of the invading swarm.
Update: Can I ship Ember and Rarity? Can I can I can I ?!?!?!
Coughneverthefinalwordcough
Please excuse me, I need a moment to pick my jaw back up off the floor.
Horizon, you magnificent bastard, I read your STORY!
5425916
You fool! Emberlight is the ONE TRUE PAIRING.
5426019 BUT I'M SAVING HER FOR DISCOLIGHT!
(seriously, I have like 4 discolight stories in various stages of completion.)
5426031
There was a time I couldn't stand that pairing. Than Baal Bunny wrote a thing.
That said, I was not entirely joking before.
*applause*
Y'know, this story has a lot more selfless self sacrifice in it. It's heart warming to see what lengths friends do things for each other, eh?
WARNING: SPOILERS AHEAD
"...Think but this, and all is mended—
That you have but slumbered here
While these visions did appear.
And this weak and idle theme,
No more yielding but a dream,"
*sigh*
The irony is, of course, I should be asleep right now, but a mixture of fatigue and illness have conspired to keep me awake this night.
I have not read the original story, and the first chapter intrigued me greatly, so I waited for the second and third to complete it all at once. I dig changeling stories and I dig Rarity stories, and this one looked intriguing and well written. Having finished it all, I must say... I am disappointed. I have a personal distaste for stories that propose immorality or dishonor as the solution to a problem. There is, essentially, a reason why we have cliches like "honesty is the best policy."
I find a core premise of Ember's plan, that ponies wouldn't accept the changelings with any charity without uniting them against a common enemy to be really really ignorant. Like, this is a show where its most fascinating characters and themes are centered around forgiveness and redemption. So inserting this weird aesop about manipulation is... weird. Also, he and Rarity were wrong, or, at least they can't make certain claims with absolute certainty. It is entirely possible that if the ponies and changelings found out about him having played everyone, they might still stay united, because people tend to pity martyrs and admire their work. In fact, that's kind of an annoying rub in retrospect. The story expects a mass of anonymous strangers to sympathize with a character who feels he cannot be sympathized with by a mass of anonymous strangers and accept this simultaneously as right. So, given all that, I feel the fic moralizing about the necessity of deception and touting the deceptive as being more clever than those around them to be... hallow.
Also, I found the meta-feint that Rarity is not a changeling to be... odd. Was it an artifact from the original story? Was she a changeling there and you wanted to mess with the heads of your original readers? It wasn't... bad, so much as it just sort of wasted time and energy on the part of the audience, and Rarity having been a Changeling might have made the story more interesting. Just, an extraneous feature, mostly.
So, I admit, the premise was intriguing, and your set-up hooked me greatly, but the payoff I found to be cluttered and if I'm honest, kind of tired and cliche. This is the same moral dilemma as Watchmen and a lot of other art looking to be or tout "moral ambiguity," and it didn't entirely make sense there and it doesn't here either. The little hangups add up and basically erode the aesop of the story. It's out of tone for the show, doesn't make sense in setting, doesn't make sense out of setting, and it's a song and dance we've seen numerous times before.
So, yeah. Sorry. Didn't work. Better luck next time.
5426178 I can't wait to see Horizon's reply to this.
I still dont quite understand what happened with Rarity.
5426178
This is my personal opinion, not Horizon's:
The reason this seems confusing is because Rarity is the other major antagonist of the piece. Ember and Rarity spend the whole story thinking that they're very clever in their lies and deceit and do their best to keep their plans from falling apart; indeed, Rarity intentionally patches up flaws in Ember's plan because her own plans are contingent upon his. Both of them think that they are being so clever in their actions that neither of them recognize that they are the problem. Indeed, once Rarity comes across important, indeed vital information, not only does she fail to share it but she actively hides it because it would screw up her beautiful plans if her friends knew what had happened. She convinces herself that she is doing the right thing because she is incapable of backing up and looking at the situation rationally from an outside, objective perspective; she has so convinced herself of her own moral superiority and that her plan was the way that she failed to examine whether or not her original plan should be entirely discarded when information came up which rendered it moot.
The true villian is deceit, and the heroes fail - Ember and Rarity play out their game successfully despite it being purely unnecessary, and Rarity, at the very least, had all the pieces she needed to realize that the game was stupid to begin with, but she couldn't put them together because she thought she was much more clever than Twilight. Fluttershy and Pinkie Pie just keep there from being too much collateral damage, while Twilight is always too far behind the game to do anything other than be played until the very end, at which point she, at least, recognizes that she is being played.
5426354
See, I didn't see Rarity as the villain. The fic seemed to be proping her up as right even though the motivations of her plan don't make sense and the plan itself is condescending and somewhat dehumanizing to her friends and neighbors. I guess if she was meant to be the villain my distaste for her actions means something worked, but it still didn't seem clear. Rarity is never called out on her behavior save once where Twilight can find no meaningful objection to it other than a declarative of "it's wrong" making her opposition look inept. Celestia seems aware of the issue but at the very least tacitly supported it by not intervening, and the fic ends with Rarity basically thinking to herself that eventually Twilight will grow up and understand she was right and Celestia's framing of the revelation as a "lesson" reinforce these two observations. One has to take context outside of the story itself to figure out Rarity/Ember were basically engaging in meaningless manipulation, and the ethical arguments surrounding Greater Good behavior are as old as human civilization, so expecting people to be resolved on that seems odd, basically. So I'm not really sure where its indicated that Rarity is acting as a villain/anti-villain as opposed to a really dickish anti-hero acting with authorial support.
If you are reading this far down in the comments, there'll be spoilers.
So, Rarity is alone in that room with Twilight? That reduces the possible explanations for what Rarity saw in her little mirror.
Yep.
Ooo, that lit a fire in Twilight.
Hahaha, I like it. Oops, but Rarity doesn't and for good reason, and apparently has a plan of her own.
Hmn, is Chrysalis developing more holes? That seems unhealthy.
There we go.
A Friendship Dungeon? Hmn.
Wait, what? Why did she panic so much about the spell or wince at it being cast if she knew she wasn't a changeling? Seems like an odd reaction. Did she think she was a changeling in deep cover?
Huh, okay.
Changeling member of the CMC is a go!
Good story, and good though confusing twist with Rarity.
How this is not featured yet?
God this was best christmas story ever that plot and subterfuge it was genius, on start I didn't like that first person but damn I can't now see how this would be good in any other way especially with that mirror thing.
It was first class story and If you write other stories on same level of awesomes then you have new very happy follower
Very interesting, as twisted and confusing as ever and wonderful til the last.
5426388
I really appreciate you speaking up. There's some irony here, in that the core theme of the story is bleeding out into the meta: the narrator is so caught up in the layers within layers that the true moral was there all along, but landed right in their blind spot.
I would not have been able to provide nearly so eloquent a summary as 5426354 did, but that was what I was aiming for. The biggest textual clue is the framing story of the Hearth's Warming pageant, which was very deliberate and (designed to be) unsubtle; we hear the entire HWE story from the POV of one of the ponies who caused the problems in the first place, and that parallel is so apt it pierces through her self-deception, if only for a moment.
But you're right, I mishandled Celestia's part, and Twilight needs a stronger voice at the end. There are elements of the text at cross purposes to the subtext I wanted to communicate. I'm gonna dive in once more over the weekend and see if I can fix, if not all of your objections, at least the primary one, and strengthen the theme TD identified. (It won't take much, but it'll take precision.)
Thank you both again. Comments like these are worth their weight in gold.
5425813
Drawing out into the story the ponies' reactions to the wedding massacre would just draw more attention to it, and distract from everything else going on.
Glad you enjoyed it! I suspect that particular piece of fridge horror is unfixable though.
5425916 5426019
You're asking me if you can ship? Darn you and your pier pressure!
...
(Seriously though, go wild.)
5426529
Ah, thanks for reminding me. Rarity's reaction to Twilight's spell is actually another big fundamental clue to what I was talking about with 5426388. (Might be worth going back and skimming that thread.)
It's another explicit moment of "Rarity acting like a villain". Obviously, Rarity isn't a changeling, and she was never afraid that she would be unmasked; in fact, the text is explicit that it doesn't occur to her it was the anti-alteration spell until after it was cast. She saw Twilight stepping forward with horn charged, and assumed the worst from one of her friends. If that's not a sign of a guilty conscience, I don't know what is.
5426238
The short, spoilerriffic version: Rarity is not a changeling. Every scene with her looking in the pocket mirror was actually her spying on Ember. When she heard Twilight say someone needed to figure out Chrysalis' plot, she upstaged Twilight to leap into the starring role, so to speak. She figured out Ember's plan to be evil to both the changelings and the ponies to push them together, and she set up a fake poisoning scene to help him sell his story.
5426693
If you want more of the twists and mysteries, keep an eye out for the upcoming The Case Of The Cowled Changelings, which just needs a little editing. If you like a little romance and poetry mixed in with the deep, rich layers, read Thou Goddess. If you want a tongue-in-cheek comedy mixed with this story's deep character reveals, check out The 18th Brewmare of Bluey Napoleon. And if you're just here to melt your brain: Hard Reset 2. 
Thank you!