Just over 1000 years ago, a great evil was sealed away at the expense of the lives of the King and Queen of Equestria. It was hoped that the force would stay locked away forever, unable to escape the confines of its prison. However, that was not meant to be.

In the modern era, Evening Primrose, a Bat Pegasus from Duskstone Peak, sets out for Canterlot to find her fiancé, Midnight Sentinel, with the help of her trusty lyre-tailed nightjar partner, Flick, and a strange tall, dark pony without a cutie mark who joins her on her travels.

Together, the three friends suddenly find themselves caught up in a war that was over 1000 years in the making. The Nightmare Door has opened and the force within it has been unleashed. Can Primrose and her friends stop it before Equestria is enshrouded in an eternal nightmare? Aside from that, who will they know who to trust when even good friends could be an enemy in disguise? How can they defeat an enemy who can look right into their minds and souls while they sleep?