The ponies of Ponyville are busily preparing for Winter Wrap-Up, with manager Twilight Sparkle unsuccessfully pitching the City Council to split the events over several days - they are very insistent on it being on a particular day.
Princess Celestia, in her vault in the Palace, dons her Mother's Crown and sees a series of strange visions - a glyphic diagram of circles and lines, a pony she doesn't know, a statement that "it all hinges on Fluttershy", and a number of other inconclusive visions. Some investigation reveals that the diagram describes a map of the Palace. Twilight Sparkle also idly doodled the same glyph on a notepad while reading, but thought nothing of it.
Days later, at a mushroom ring deep in the forest, a Seelie (more or less "good") faerie creature in the form of a pale green-eyed earthpony with a long white mane and tail appears. This fae has no name that she has revealed, appearing in the feed as mlp____ or ???. The faerie has awoken earlier than most, who awake with the Spring every year in the forest, possibly connected to winter wrap-up.
The fae, speaking obliquely, explains to Fluttershy that she is on a mission to find three of good heart and three of impure heart, and is evaluating ponies she meets. She does not explain what she plans to do with these ponies, only that they are needed for something called the Dance.
Elsewhere, an Unseelie fae creature is stirring, one that instills great fear in the pale green-eyed pony with the white mane, this one is also nameless but referred to with the sound of a distant crow's caw. He is a dark faerie king, lord of wild magic and the hunt, and may awaken with the Spring as well unless the pale faerie and the ponies of Ponyville can prevent it. Crow's Call may be responsible for a remote castle on the edge of the Everfree Forest being overwhelmed late one night with dry thorny bramble vines that tried to surround and imprison all inside, before the guardponies fought off the attack.
The pale faerie has spent several days recruiting animal spies, such as the cat Pangur Ban (@mlp_Pangur) and enjoying life among the mortal ponies, playing occasional tricks and conversing with ponies to determine their purity of heart, and gathering candidates for the Dance. She has been spotted a few times, but is able to use illusions and jedi mind tricks to conceal her position or make mortal ponies forget they saw her.
The pale faerie has visited many in Ponyville, to test the purity of their hearts. Upon her visit with Daisy, she deposited a satchel of seeds in the care of the Earth Pony. Out of curiosity, Daisy made her way to the Froggy Bottom Bog to look for some Poppy-See-Bright. Once there, she was confronted by a large hooded pony with a red coat. The pony warned Daisy to follow ??? but to be wary as to full trust. Daisy was instructed to plant the seeds given to her by ??? and by the RedCoat in Trottingham days earlier near one another and safely. Right now, they are planted in her greenhouse behind an iron gate, near her other secrets.
So far the candidates are:
mlp_Phazer, mlp_Blueblood, unnamed candidate for the evil
mlp_Fluttershy was to be the Lady of the Dance, the central figure of the ritual however she has been turned into a tree and is immobile.
The pale faerie dislikes unicorn magic, considering it noisy and unpleasant, and has avoided the Treebrary and interacting with Princess Celestia as of yet, considering the princess oafish and magic-heavy unicorns to be too graceless for her purposes. The pale faerie has her own magic powers that are based on probability, mind, and nature, but is vulnerable to cold iron, fire, mirrors and technological items. She doesn't care to enter dwellings unless invited.
Meanwhile, Twilight Sparkle has had her days filled with stress, planning Winter Wrap-Up logistics and signing up volunteers as well as running the Treebrary and researching faerie magic by order of Princess Celestia. Her research and the sporadic sightings of the fae around town have led her to conclude that the connection between the visions, the fae, and Winter Wrap-Up itself is deeper than she thought. Twilight travelled with mlp_Hyperia to the archives in Town Hall to find records of the Compact - the original centuries-old agreement between the earthpony founders of Ponyville and the faerie-folk of the Everfree Forest, where they agreed to steward the seasons as long as no sorcerous means were employed. In an iron room deep in a tunnel underneath Town Hall, she found the original copy of the Compact, sealed with both Pony and Faerie seals, and took it with her back to the Treebrary for perusal.
That night, while Twilight, Spike and Hyperia were reading the scroll in the Treebrary, a flock of ravens burst into the room and stole the scroll and flew off, pursued by @mlp_Aloysius the owl. The Treebrary was then visited by ???, who filled in Twilight and the others about the Dance and the status of the agreement - if it is broken, then the Sleeper will awaken and the ponies will no longer be able to control the weather in Ponyville (among other bad things). The scroll itself is not magical, it's just a copy of signed contract - it remains in force as long as its conditions are met by the ponies.
The scroll was rescued in a dramatic chase by Aloysius, @mlp_SmartyPants, @mlp_Jim and the Cake foals, @mlp_poundcake and @mlp_pumpcake, and Twilight returned it to its original location.
The same day Princess Celestia was granted an audience with the queen of the faerie Seelie Court, mlp_Titania. The faerie queen agreed to let a trustworthy earth pony or pegasus attend The Dance, as no unicorn magic is allowed. Princess Celestia tapped Orson to be her proxy and set him on a task to spy on The Dance and create an iron-free microphone and earpiece so she could listen in and tell him what to say.The night before the Dance, Fluttershy was turned into a tree - she didn't mind a bit, and was taken to the Green, the site of the dance deep in the forest, where she grew to enormous size and acted as a dome over the Green, the entire dance revolving around her as the central pivot.
The night of the Dance, the ponies were invited to watch and all the Faerie folk came out of the woods to watch and participate. The Candidates: Esmeralda, Daisyfloral, Roseluck, Blueblood, Sniper and Phazer were placed within circles of flowers, and asked questions by the Seelie representative ??? and the Unseelie representative mlp_Crowscall, represented as a dense swarm of fluttering crows. The questions would be used to discover which of the ponies would become Changelings and leave the pony world forever.
After a round of questions, it was apparent that Crowscall was not taking them seriously and the final question of the Seelie was turned to Orson, Celestia's representative: mlp____ asked "What is my true name?"
Celestia realized that while on Equestria she had naming power, and assigned the name Seelia to her. Seelia accepted this and became a mortal pony, fulfilling the Compact for a century and realizing her long-held wish to become a normal Earthpony.
Crowscall had one final question, and asked Fluttershy if she would remain a tree forever and be taken to Fairyland with him - she refused, saying while being a tree was of of her hearts' desires, she needed to stay in Equestria and take care of her animal friends, and she'd miss her pony friends too much. Baffled, Crowscall attempted to simply kidnap Daisyfloral via a crow proxy. The power of friendship inside Daisy singed the Fae King, and his form was kicked by Colgate as Twilight and the observing ponies and faeries beamed friendship magic at him. Taking advantage of the Kings weakness brought about by the power of friendship, Daisyfloral tossed the special flowers she had grown for the ceremony at Crowscall, banishing him from the Green.
Then there was a party!
Mlp____ is now mlp_Seelia, and is a normal Earthpony without magical powers, but with centuries of faerie knowledge. She may act as liaison between pony and faeriekind.
By Faerie law Fluttershy is to remain a tree until Winter Wrap Up takes place in a week. She has been moved back to just outside her cottage.