On a peaceful day with nothing to do, Twilight realises it's been a while since she's last seen her own friend Sunset Shimmer. When she goes to visit her, Sunset confesses that she's ready to return to Equestria and make amends with Princess Celestia. Once back in her old homeworld, Twilight, Spike and her friends accompany her to Canterlot to do so.

Unfortunately their plans are put on hold when in the desert of Somnambula, in the deepest tombs, an ancient evil awakens. Someone that has deadly plans for the ponies of Equestria...