Years ago Nightmare Moon returned to Equestria to bring her eternal night. She appeared in Ponyville without warning and one unicorn stood up to challenge her, but she tried to do it alone and she failed. Celestia was defeated then banished to the moon like Nightmare Moon once was and the lone unicorn went into hiding ashamed of her failure. Now Equestria is ruled by Nightmare Moon, and she has turned the simple kingdom into a thriving empire. This is the story of her daughter Diana, and her journey to discover the truth about her mother's origins and bring together the heroes of Equestria that were needed all those years ago in order to stop her tyrannical rule.