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.

When she catches a bad case of pegapox, Rainbow Dash cannot fly up to her cloud home. Grounded and quarantined in Ponyville, she is taken in by Rarity and Sweetie Belle, who vow to nurse her back to health. Can the pegasus survive her well-meaning caregivers long enough for Twilight to find a cure--and why is the weather turning so weird?