Cadance locked herself in the bathroom.
One would perhaps not see anything unusual about a Princess valuing her 'me' time and the chance to freshen up without being disturbed, but this was a bathroom in the Crystal Castle's eastern annex and two floors below the Royal Quarters. It was also in an area under renovation and not currently connected to the water mains. The interior was half-finished at best: a silver claw-foot bathtub unconnected to anything; an empty vanity over a sink without taps; the crystal walls bare and unpolished. Thus the room being an exceptionally poor choice for a quick shower, an observer would question why the Princess of Love was locking herself in.
Then again, the same would be asked about why somepony was watching the bathrooms in an unoccupied section of castle at two in the morning.
So unseen by prying eyes, Cadance locked herself inside the bathroom. She stopped there for perhaps a minute, listening at the door for hoofsteps to ensure she was truly alone. When it remained silent save for her own breathing, she finally relaxed. Reaching into her saddlebags, her magic lifted out a beautiful hoofmirror: gilt rosewood, accented with perfectly cut emeralds. Earlier today she had found it on her nightstand - which under other circumstances would have been a mystery, as she owned nothing like it. But she knew the plan, and so she had simply kept it safe until now.
Setting the mirror on the floor, Cadance stepped back and took a steadying breath before loudly stating: "Mirror me, my mirror."
The hoofmirror trembled for a moment - before bursting into green flame. It reformed swiftly into an identical copy of Cadance, perfect and exact save for a single detail: the new Cadance looked at her counterpart with green, cat-slit eyes. The two stared at each other for several seconds, tense and waiting.
"...You need to say the counter-phrase," said the original Cadance in an even, careful voice.
The newer Cadance grunted and rolled her eyes with irritation. "Eros tastes like bubblegum and philia like peppermint, but agape is the sweetest of all." She growled a little before glaring at her double. "I don't know why you insisted on a counter-phrase. Who else could I possibly be?"
"That's how it works in all the spy novels, Chrysalis." Cadance couldn't help her gleeful smile. "Plus it's cute when you say it."
Chrysalis' tail lashed. "Can we get on with this? The longer you delay, the more likely we are to be caught. And I'm certain you don't want any of your precious ponies harmed over your little plan."
"Our plan," Cadance replied with a huff. "And I just want to make sure we both understand what we're doing. Communicating through coded letters is one thing, but speaking in pony is much clearer. And Shiny has really drilled into my head that it's worth double checking your plan before putting it into action."
With a further grumble, Chrysalis plopped her (temporary) princess butt down on the side of the non-functional tub. "This is a pointless delay, but arguing it with you will just take longer. So fine, we'll go over it again."
"Thank you." Cadance turned around, showing her back to Chrysalis - while still keeping an eye on her in the mirror mounted on the vanity. "So we switch places here. You return to the Royal Quarters, while I sneak out via the security gap I arranged during the renovations."
"And then you pick up the train ticket I reserved under a cover identity," Chrysalis dryly continued.
Cadance clicked her tongue, scolding the changeling queen. "We're not to that part yet! The order of operations is important."
Her only response was another sarcastic eye-roll from the Queen.
"You spend the rest of the night with Shiny, then in the morning you get up with him and have a family breakfast with Flurry Heart." Cadance then paused, looking to her companion.
Chrysalis sighed before repeating herself. "And then at about the same time, you pick up the train ticket I reserved under a cover identity."
Things went silent - save for the sound of Cadance's hoof tapping on crystal.
"Ugh." Chrysalis started again. "And then you pick up the train ticket I reserved under the cover identity of Ladybug Lemonade, leaving aboard the 7:25 train to Hope Hollow."
Cadance cleared her throat. "The 7:25 train to Hope Hollow via what?"
"Via Rainbow Falls, is this really necessary?" Chrysalis jumped to her hooves, sending a resounding crack through the otherwise silent room. "You are testing my patience. I could easily place you in a cocoon and none of your precious ponies would find you for days."
Chrysalis expected Cadance to go on the defensive like so many ponies before her: to spin around, legs wide and wings spread as she spit defiance and impotent threats. Yet the alicorn simply stayed where she was, watching Chrysalis in the mirror. "And then we're right back to where we started. You're constantly on the run and I'm constantly looking over my shoulder for you. The whole point behind this temporary switch is to reach a deal where my family gets some peace and you get to concentrate on something else."
"Somepony else," Chrysalis snarled. Then - realizing she had done so - straightening her back and recomposing herself. "Fine. If it means I can focus my attentions on Starlight Glimmer, then this entire idiotic dance will be worth it."
Twisting around, Cadance practically high-stepped the few paces over to Chrysalis. "Is that aaaaaaall?" Her sing-song voice playfully warbled as she nuzzled her head along her mirror image's neck. "Because I'm pretty sure part of why you agreed to this was so that you could spend a few days basking in all the love and happiness of Hearth's Warming with my family."
A reflexive sneer leapt to Chrysalis' lips - but she also didn't deny it. Instead, she gave her own counter. "And you expect me to believe that you're keeping your end of the bargain for fun?"
"I should be asking you that." Cadance pulled away so she could look eye to eye with the Queen. "Thorax and Pharynx went to a lot of trouble to set up a clandestine get-together just so they could see you for the holiday. I don't mind spending it with them, but I also don't understand why you're trying to get out of it."
Chrysalis scoffed. "You mean why I'm not coddling them? Please. It isn't even a changeling holiday!"
A slight frown came to Cadance's lips. "It is now."
She received a glare in return. "Are you going to leave or what?"
Petulantly, Cadance pouted at her counterpart. But - finding nothing but irritation in return - she eventually sighed and nodded. "Alright, alright, I'll go. Just be careful. The Sparkles will be here around noon, and they can be a bit… intense when it comes to the holidays. They mean well and it's better now that Twilight isn't with them all the time, but–"
Chrysalis held up a hoof. "Just go. You've already wasted too much time as it is, and if you get caught and ruin this I will be extremely displeased."
The urge for sarcasm was high, but Cadance knew she could only needle Chrysalis so far before triggering a rage. So she gave her counterpart a nod. "I'll see you at the rendezvous in five days."
Then she teleported herself to a pre-arranged quiet spot on the castle's outskirts, while the disguised Chrysalis trotted out into the halls as if she belonged there. And for as far as anypony knew - she did.
The rendezvous five days later was not quite so lowbrow as a half-renovated bathroom. Not at least partially because Cadance couldn't simply disguise herself as a mirror and be smuggled inside. So - they required a different approach.
Thankfully there was an easy and obvious solution: after a rough holiday with family, Princess Cadance went to the Crystal Empire's day spa and reserved herself a private sauna room.
It was precisely what one would expect to be given to a Princess: large enough for ten ponies to lay on the smooth red cedar benches that surrounded the crystal basin full of hot stones. The water in the bucket to be poured over top was filled with rose petals, and the staff had additionally left a bottle of flavored water (just a hint of orange blossom) in case their Princess over-exerted herself.
Relaxing on the bench in a languid drape, Cadance let her eyes drift mostly closed as the warmth of the steam seeped into her muscles and wicked the tension out of them. In fact, the Princess didn't even bother to open her eyes when the door opened and another pony slipped silently in.
Both sat together in silence for long minutes, letting the steam swirl as tension built. Finally, the Princess opened one eye to look at her new companion. Cadance looked back with an eager small full of giddy anticipation.
Heavily, the Princess sighed. "You know it's me. I literally look identical to you. Who else could I possibly be?"
Cadance shook her head. "Well no, I can't know it's you. You haven't said the code phrase yet."
The 'Princess' growled. "Fine. Mirror me, my mirror."
Cadance almost couldn't get out the response through her giggles. "Eros tastes like bubblegum and philia like peppermint, but agape is the sweetest of all."
Now (needlessly) confirmed, Chrysalis rolled her Cadance-like eyes. "This is all so stupid. Why is it that I am the one who led a civilization of expert infiltrators, but you're the one who's playing spy?"
"Because I still understand how to have fun," Cadance fired back. Crossing her hooves, she wiggled into a more comfortable position. "Now! Before you start grumping and grumbling, I'm going to ask you a question. Did you enjoy yourself?"
Chrysalis' sneer melted away as the question was asked - and she let out a frustrated, regretful sigh. "Yes."
Nothing was said for another minute as one side tried to avoid the subject and the other patiently waited for further details. Eventually, Chrysalis relented with a grumble that was done more out of obligation than actual feeling. "It was… nice." She shifted uncomfortably, feeling Cadance's eager eyes boring into her. "I haven't had so much love since your wedding."
"And?"
It was a leading question, but she knew what Cadance was asking. She still tried to evade. "And it was nice."
Cadance craned her neck forward, trying to ineffectually loom over her disguised double. "Nice how?"
"It was nice!" Chrysalis spat the words with venom more from frustration than actual anger. Then she pulled back, glowering at the steam-slick wall. "I will admit that I initially expected betrayal. That I would awaken in the morning to find your mate had attempted to imprison me or that you had snuck Starlight Glimmer in to ambush me as I rose." Her eyes darted to glare briefly at Cadance. "Which would not have ended well for any of you."
Rather than take the bait, Cadance simply smiled innocently. (She, admittedly, could not deny that she hadn't considered it.)
"But as the time passed, it became obvious your offer had been earnest," Chrysalis continued, eyes focusing once more into the middle distance. "I will admit, I let my guard down."
When there was no immediate continuation, Cadance gave her companion a gentle verbal nudge. "It was lovely, wasn't it. You've been on the run for quite a while and I know you haven't been able to relax."
Those kinds of emotions were weakness. Chrysalis would never admit to weakness. So she dodged around it with a huff. "I was presented with opportunities I haven't had in some time, yes."
The admission was good enough for Cadance - she moved on. "Hearth's Warming went smoothly? Night Light and Twilight Velvet didn't cause any problems?"
Chrysalis erupted into slightly mad laughter. "Oh, so many problems! Several of which I encouraged, as it shall be you cleaning up rather than I." With a sly smile, she dropped a hint towards one of the bombs awaiting the Crystal Princess. "Your father-in-law introduced me to bingo. I introduced him to Boggle." She paused for a moment in victory before realizing that Cadance had no idea what that was. "It's a game," Chrysalis explained. "You get a random bank of letters and have to assemble them into as many words as possible within the time limit."
"Oh!" Cadance's eyes lit up. "Like Countdown?"
The changeling stared at her for a long, long moment. "I suppose?"
"And teaching him. That's… bad?"
Scowling, Chrysalis rose and turned so she could more effectively glare at Cadance. "Yes! Because he's married to an editor! And now he's going to get into arguments with his wife because she'll keep correcting his spelling! Neither of them shall know peace!"
Cadance owlishly blinked. "Um. Okay, I'll take your word for it…"
With a grouchy harumph, Chrysalis slumped back down to pout. "If I had known you would be so blase about it, I would have taught him Monopoly and ruined your family forever."
Reaching out with her magic, Cadance poured another ladle of water on the hot stones in the center of the room and unleashed another cloud of steam. "Well, thank you for not doing that then. I like my in-laws and they give Flurry the nicest presents."
"Oh, it was a beautiful one this year too!" Chrysalis' emerald eyes lit brightly. "It was a stained glass sliding puzzle, that when you solved it created the image of…" And realizing her enthusiasm, the changeling Queen trailed off to an embarrassed cough. "It was nice."
That, of course, resulted in more giggling from Cadance.
Chrysalis quickly tried to change the subject. "So what about my wayward children? Were you able to fool them for the entire holiday?"
"Oh, they figured it out in under five minutes," Cadance said with a dismissive wave. "I think it only took them that long because they couldn't believe I had willingly switched places with you. Which to be fair is a fairly illogical situation to an outside observer."
It was precisely this moment that the phrase 'incredulous stare' had been invented for. "And you stayed?"
"Of course!" Cadance beamed happily. "We had a great time. I don't get to see Thorax nearly as often as I used to, and it was a chance to get to know Pharnyx. Thorax is practically family, so meeting his brother is something I've wanted to do for a long time. We spent most of the holiday enjoying the local celebrations - I haven't had the chance to be in a small town for Hearth's Warming since before I was a princess!" Her happy sigh said it all. "I love my family, but it was nostalgic and a good chance to decompress. Not being a Princess for a while was enjoyable, and Hope Hollow was remote enough that I could just be a pony."
Chrysalis continued to stare at her, not entirely sure just what to say in response.
And unstopped, Cadance continued as if it were nothing. "I brought their presents for you, though. They're in the cream-colored hoofbag outside - third cubby in the second row." The gleam in her eyes told volumes about how she wanted to gush about what they had gotten for the wayward Queen - but that would spoil the surprise.
"...thank you," was all Chrysalis could manage, still not entirely certain how to react..
"You're welcome." Cadance rose from her seat on the bench, coming up beside the changeling. "This really was nice, Chrysalis. For both of us, I think." She paused just long enough for that thought to sink in. "In fact - I would like it if we could keep it up."
Chrysalis' ears flattened. "What?"
It wasn't a denial. Cadance verbally pounced. "A long term truce. This proved we could live with each other, Chrysalis. You talked about how you wanted to focus your attention elsewhere, and I said I wanted to stop looking over my shoulder." She half-stood, energy and eagerness overflowing. "We could take this holiday truce and make it permanent. We stay out of each other's way, and we both keep getting what we want."
The sauna was silent save for the hiss of water on the coals. Then - a grumble. And a grudging nod. "Yes. Consider a truce to be agreed upon. I shall no longer target you or your immediate family - your husband and your daughter are safe. As is your kingdom." She momentarily paused before quickly appending her statement. "If one of you places yourself against me in battle, I shall not hold back! But as long as you do not, I shall leave you be."
"In exchange, I won't directly oppose your actions," Cadance said in return, keeping her best Celestia Negotiating Voice on. "And I will personally step down the Crystal Empire's changeling detection efforts, so it can be a safe place for you - so long as you do not harm or otherwise endanger any of its ponies."
Chrysalis nodded once - sharp and firm. "Then we have an accord." She was engulfed in green flame as she cast Cadance's form aside and turned to the pale green form of Shutterbug. "I will begin communication for our next exchange."
Sitting back down to continue enjoying the steam, Cadance nodded. "Agreed." The firm face of negotiations faded to a softer smile. "Happy Hearth's Warming, Chrysalis."
Pausing halfway to the door, Shutterbug glanced back. And while she tried to sound sarcastic, there were the hints of a smile in the corners of her lips. "Happy Hearth's Warming, Princess."