For centuries the seas of Equis have been plagued by pirates. None more fearsome than the Crew of Eternal Night. For years ships sail in fear of Eternal Night and her captain, Nightmare Moon. Princess Twilight Sparkle, tired of being overlooked in favor of her older Sister Cadence, joins the crew of the Harmony under the guise of a unicorn named Velvet Light. She is soon introduced to the ship's crew and discovers that they are on a mission from Princess Celestia herself. A mission to hunt down and capture Nightmare Moon.