One thousand years ago the Mare in the Moon first appeared, Celestia was forced to banish her sister to the moon. Generations later, Equestria has changed, Nightmare Moon is forgotten and the Mare in the Moon is just a myth told to little ponies.

All of Equestria is jarred when the myth returns. All of Equestria, save for two. Celestia herself and a pegasus mare named Shadow are the only ones that expected this to happen. Unexplainable urges to venture deeper into the Everfree Forest along with worsening headaches drive Shadow to find out the truth.

She finds the truth, but something else finds her first.