Rainbow Dash's past has finally caught up with her. She had feared before that it would come back and hurt her friends, but she puts on a brave face and pretends that everything is alright. Though, her friends start to notice that Rainbow is looking more exhausted than usual, and she's been training harder and much too frequently. Then, just as the truth is revealed, no pony expected such darkness to cascade over Ponyville. Soon, all of Equestria will be suffering from a past mistake. As mistakes go, will Rainbow Dash be able to learn from it?