Luna has been through a rough past, feeling unappreciated, depression and her experience of turning into Nightmare Moon.

But one day, a visit to a magical cave in the Everfree Forest changed everything when Celestia decided to bring a little souvenir home with her.

Equestria's only help leads to Luna, Celestia's sister who has no control over the situation. She too, has gone through an evil phase, only to be stopped by The Elements of Harmony.

But with the elements no longer in control with Twilight and her friends, she has to go on an unexpected journey with Twilight and Princess Cadence, to save Equestria from Solar Flare, her sister.