The Summer Sun Celebration has gone off without a hitch, leaving Twilight embarrassed and confused. She is sent to remain in Ponyville to learn about friendship, the most powerful magic ever. However this task is interrupted by an unwanted guest. Not only is Twilight forced to put up with her new houseguest, she's starting to feel a change coming over her, taking over her mind. Can she resist the call of the night, or will she fall entirely into the grasp of Nightmare Moon?