The most trusted and faithful student of the benevolent ruler of Equestria, Twilight Sparkle, has been chosen to become the ambassador to Princess Celestia's oldest friend. With the help of her new friend, the young unicorn will discover a great and terrible secret about the past of Equestria, that will soon come to threaten the present. Twilight and every pony in the land must ready themselves against the coming darkness if they are to prevail.