"Queen Seondeok" tells the story of Princess Dae-Man (played by Lee Yo-Won), who was abandoned as a child due to an inauspicious prophecy. Through relentless effort and navigating power struggles within the palace, she grows to become the first queen of Silla — Queen Seondeok.
In a situation where Mi-Seok (played by Ko Hyun-Jung) wields great power in the palace, King Jinpyeong and Lady Maya gave birth to twin daughters. However, for the king, the birth of twins was considered extremely unlucky, as it carried the ominous sign of "the end of the sacred royal lineage." Reluctantly, King Jinpyeong ordered that the younger daughter, Dae-Man, be sent away, but Mi-Seok secretly dispatched assassins to pursue and kill her. At a critical moment, Dae-Man was saved by Hwarang legend Moon-Nu, who devised a plan to rescue her and handed her over to So-Hwa, one of King Jinpyeong's maids, for care. So-Hwa took Dae-Man to the desert regions of China, raising her in a small inn.
Princess Dae-Man's greatest rival, Mi-Seok, used her exceptional beauty to win the favor of King Jinheung and gain control over the palace. Ambitious and cunning, after King Jinheung's death, Mi-Seok installed the young King Jinpyeong on the throne. When King Jinpyeong's wife gave birth to twin daughters, Mi-Seok planned to use the birth of these twins to further her schemes...