Nightmare Moon defeats Celestia in the original battle, and sets herself up as queen. Fearing rebellion, Nightmare Moon uses her powers to take away all the unicorns' magic. Well, almost all of them.
With her new apprenticeship under Nightmare Moon, Empress of Equestria and Queen of the Eternal Night, the orphan filly Twilight Sparkle plunges head-first into the conspiracies, secrets and intrigues of the Empire.
Nightmare Moon won a thousand years ago, plunging Equestria into perpetual night. Now, as Princess Luna's student, Twilight Sparkle must contend with Celestia's unexpected return as a familiar group of ponies are thrown into conflict.