Young musician, Octavia is invited to conduct the mares' choir for the coronation of Twilight Sparkle, soon-to-be princess, and decides to invite a young colt, Featherweight to join. Though the event proceeds with no problems, preceding the coronation is the disappearance of Princesses Celestia, Luna, Twilight Sparkle, and Cadance, leaving a mystery to be solved by the mare and her protege.