Until the Day of Flowering Prince I-Yeon of Yeonghwaguk is appointed as a part of a peace envoy to Vesthal, after the two countries strike a treaty following a long war. The free-spirited prince is shocked by the sudden responsibility, but determined to try his best to keep the peace. When I-Yeon arrives, he meets his counterpart, Crown Prince Calix of Vesthal, whose cold demeanor points to his lack of interest in being friends, much to I-Yeon's chagrin. But after a sudden accident, the two are brought together, closer than either of them ever expected. Can the two royals keep their budding relationship under wraps and maintain the fragile peace between their kingdoms?