Celestia has tragically died and the dead have started to rise and attack the living as consequence. Despite the attempts of the other princesses, the elements of harmony and brave ponies who risked their lives, the dead prevailed. Continuing to plague Equestria for generations, killing thousands.
One unfortunate mare from the first invasions comes across a certain element of harmony who once saved her life, only this time she's part of the plague.
Edit: I would suggest reading from the start since it has been so long since the last chapter
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