A long time ago, two godlike beings were the first to channel the powerful energy known as magic. But a catastrophic incident forced them to be sealed away, eternally trapped deep in the earth, in the core of all magic.

Many eons later, Princess Celestia mysteriously falls sick. She is suffering from a severe magical imbalance, one never seen before. This can only mean one thing: the powerful seal that keeps the two beings in the earth is fading, and soon, they will break loose.

The only solution is to find an ancient journal, one that belonged to Star Swirl himself. Twilight and Cadence will travel to the edges of the world to find this journal, which contains the spell that created the seal. But there are many secrets that have been hidden from them, and everything they know will change.