Countless years had passed since King Sombra started haunting the Crystal Empire. The citizens were listless, forgetful; but when the mane 6 started investigating, truths were uncovered. Truths that were hidden for many, many years.
King Sombra, the tyrant of Crystal Empire is back, only to be imprisoned by princesses and put through reformation with Twilight Sparkle as his teacher. Can somepony with heart as black as night be reformed? Twilight believes so.
A gem containing what remains of King Sombra has been found. Now that Twilight has stepped into her role as 'Princess of Friendship' she takes it as her responsibility to help Sombra or rid Equestria of his evil once and for all.
All is well until, one by one, the inhabitants of Ponyville begin acting… strangely. Shaken by a terrible feeling of dread, Rarity believes she may be the only one left to save everypony from the rising darkness.