When news of pony disappearances reaches Canterlot, Princess Celestia implores the girls to travel to the neighboring country of Saddellia, a kingdom of earth ponies ruled by a brutish king. Eagerly accepting this mission, they make the journey and, along the way, meet and save the crown prince of Saddellia, Prince Linden.

Things become difficult when the young heir becomes smitten with Rainbow Dash and royal trickery traps the two in a marriage betrothal. As the pegasus struggles with her growing feelings for Linden, she and her friends quickly learn that there are dark secrets being kept in Saddellia and they all must tread carefully if they are ever to go home again.