Twilight Sparkle has ruled Equestria for over a thousand years. From her throne atop the floating city of Concord, she enforces ruthless harmony over the handful of surviving settlements. But Twilight is afraid: Equestria's survival always hangs by a thread, as enemies more ancient than the Alicorns threaten to return and devour what she has built.
Twilight selects her star pupil, a young unicorn named Star Orchid, to travel down from the perfect city of Concord into the dangerous ruins beneath, so that she might locate these forces, and help Twilight to destroy them. Only when every threat to Equestria is finally dismantled will she be able to rest. Until then, there is much left to purify.