Twilight returns to Celestia's and Luna's old Castle to find anything on the Box she and her friends discovered when they sacrificed the Elements of Harmony. Looking for information, she discovered a note revealing the location of a book. Twilight was exited!...until she found that the book was located in the dungeon. She investigates it, and from there well...things go from good, to bad, to shit, then to...creepy and scary. Everything in the castle makes it seem like Twilight's having a Nightmare.
Or is she?
Twilight thinks she's having a Nightmare, but an unexpected pony shows up, and Twilight can't believe who it is; Nightmare Moon! How can she still be alive?!

But then, there's that stallion with the blank face that keeps following her, stalking her.
What exactly's going on here?
Who is the Nightmare, and who is the Reality?
The answers will be revealed in the Nightmare Castle!