A human awakes to find he is no longer in his own world, even, in fact, his own body. Unfortunately, this has brought the attention of an old and ancient evil that has slumbered since before the appearance of the ponies of Equestria. Stealing a part of the newcomer, it gains back a body it has long sought.
Twilight is now tasked with raising the colt, whose mind has changed since a part of himself was torn away, fractured and is now the physical and mental equivalence of a young child. While her friends, and even the princesses search out this new threat.