To prove dark magic can be used for good, Princess Luna transformed the small town of Hollow Shades into a towering metropolis and structured it around the magic of the night. After all, the area is a natural source of dark magic, and the batponies have lived there for millennia without incident, even if legend claims it hides the gateway to Tartarus itself.
However, some legends are best left untested.
When cataclysm strikes and Tartarus is inadvertently opened, what will one little pony and her friends do when they discover that the monsters hiding in the darkness may very well be nothing compared to the darkness within themselves?