All seems well in Equestria. A hesitant peace has settled over the land in the years following the Storm King's defeat, and four new alicorns have claimed their titles: Flurry Heart, Princess of Peace; Iolite Sparkle, Princess of Secrets; Marmora Sparkle, Princess of Tides; and Charon Sparkle, Prince of Shades.

Meanwhile in the Crystal Empire, a cult dedicated to practicing the magic of the dead King Sombra grows in secret, led by a unicorn named Onyx Shard. Onyx, wanting to 'reclaim' the Empire in the name of his posthumous mentor, has begun subtly warping the minds of his followers and urging them toward this goal. They plan a brash attempt to steal the Crystal Heart, hoping to destabilize the Empire enough to allow them to rise and spread their influence.