After the Mane 6 return from babysitting Twilight Sparkle's niece Flurry Hearts, they discover a great illness surrounding Starlight and her new friend Trixie, which could endanger all of Equestria.
With help from the Cyber Trio, they go on a quest to find the only cure, the Dark Essence.
But their path hold a secret that's longer than Equestria exist...