While Chrysalis, Tirek and Cozy Glow try to figure out how to activate the bell, Grogar sets out to the Castle of the Two Sisters to confront the spirit of the Tree of Harmony.
Something has petrified the Everfree and all its creatures, giving an opportunistic centaur the means to reclaim his lost power. Faced with the extinction of life and magic, Equestria's heroes rally once again.
Twilight wants to break the curse of immortality to pass with her friends. But first she must find a Successor to take her place. Can she do it or does Equestria need her to stay? What tests await candidate Luster Dawn as an ancient villain returns?