Celestia notices that since her return from the moon, her sister hasn't been acting quite like herself. Though at first she assumes that this is because Luna is upset and broken by her exile, she soon realizes that this isn't consistent with the rest of her behavior.

After some coaxing, Celestia manages to convince her sister to tell her the story of what happened in the years leading up to the Nightmare Moon incident.

I try very hard to remain completely faithful to FiM lore, this story is set during a historical event that is well described in the show, but nothing in Midnight Blue is incompatible with anything described in the book. Instead, besides the story itself, Midnight Blue provides additional history to Equestria between what is described in "hearth's warming eve" and what is described in the first episode.

Midnight Blue is the first of (hopefully) a series known as The Harmony Volumes. I have outlined 2 other stories in the collection, and I will reveal the topics as I release more chapters of Midnight Blue.

Thanks to Nick Carey for editing help

Edit: I didn't realize it until now, but the animation/song "Children of the Night" by Spirit and Lion was fairly strong inspiration for this story. When I first saw it, about a month before starting writing I think, I loved it. But then I forgot about it, but I guess it was still impressing enough upon me to influence my creative mind. I'd like to thank Spirit and Lion for giving me a seed upon which to a large history upon which this story is based.