In the Moon Flower Kingdom, a realm inspired by historical China, the prevailing approach to healing relies on superstitious rituals that yield limited results. When Crown Prince Keiun travels to Ran Province, he and his attendant Shiei are ambushed by highwaymen secretly dispatched by the concubine Ro. Wounded and desperate, they are directed to a local doctor named Koyo. Assisted by her capable assistant Shingdam, Koyo performs an unprecedented surgical procedure that saves Shiei’s life. Her advanced medical knowledge and deft hands astonish the prince. In a land where illness is traditionally banished through ceremonies, Koyo’s practical skills represent a revolutionary departure.

To properly compensate her and to bring her expertise to the wider kingdom, Keiun brings Koyo and Shingdam to the imperial capital. He hopes she will teach others and improve public health. However, the beautiful, eccentric young doctor quickly faces resistance from court officials and traditional healers who view her methods with suspicion. Meanwhile, the prince remains a target of political conspiracies that threaten his life and the stability of the realm. As Kayo navigates the treacherous court, she must prove the value of her medicine while unraveling schemes that entangle the imperial family. The series follows her journey as she treats complex ailments, forges alliances with Keiun and his loyal retainers, and challenges deep-rooted traditions, all while shadowy forces work against them.