A legend older than Celestia itself tells that long ago the creatures of Equestria faced oblivion and survived, but that created the world as they know it today.

The Valley of Eternal Dusk is a place where dangerous magic inhabit and creatures beyond reality predate. Only the mighty city of Diomedia and its three counselors are the only barrier between the horrors of the Valley and the world, but strange activities are occurring in the Valley and Celestia has entrusted Twilight and her friends to assist the Council of Diomedia in the investigation of this strange phenomena.

In their journey the Mane Six will meet Prince Crimson Dawn, co-ruler of Diomedia and one of the guardians of the valley. But things will be hard for the Mane Six as Diomedia is a deeply divided city where counselors have kept the peace by sheer force of will. Not only the Mane Six sill deal with the phenomenons in the valley but as well with city filled with never ending mysteries where you can't trust even your own shadow.

This may be their greatest task yet.