"Queen Seondeok" tells the story of Princess Dae Man (played by Lee Yo Won), who was abandoned as a child due to an ominous prophecy, and through relentless effort and power struggles within the palace, grew up to become the first queen of Silla - Queen Seondeok.
Under the circumstances where Mi-seok (played by Ko Hyun Jung) held 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, carrying the omen of "the end of men with sacred bones." Helpless, King Jinpyeong had no choice but to send away his second daughter, Dae Man. But Mi-seok secretly sent people to pursue and kill her. At a critical moment, Dae Man was saved by the legendary Hwarang figure, Ven Wu, who then handed her over to be raised by one of King Jinpyeong's maids, Cho Hwa. Cho Hwa took Dae Man to the desert regions of China and raised her in a small inn. Dae Man's greatest enemy, Mi-seok, used her extraordinary beauty as a weapon to gain the favor of King Jinheung and thereby seize power in the palace. Ambitious, after King Jinheung's death, she installed the young King Jinpyeong on the throne. After King Jinpyeong's wife gave birth to twin daughters, Mi-seok planned to use their lives to threaten him and directly seize royal power. Unexpectedly, Ven Wu and Cho Hwa saved Dae Man, thwarting her plans. Despite holding great power, Mi-seok did not abandon her quest for the throne and plotted to have her husband ascend it. Thus, she saw Dae Man's twin sister, Princess Tae Ming (played by Park Yi Jin), as a thorn in her side. Under Mi-seok's rule, Princess Tae Ming, possessing extraordinary wisdom and quick judgment, did not easily reveal her true nature but always showcased her leadership qualities at crucial moments. Although Princess Tae Ming married Kim Yongsu (played by Park Jeong Chul) and bore a son, Kim Chun-chu (played by Yoo Seung Ho), she developed feelings for Kim Yu-shin (played by Yeom Jae-hyeong), who had once saved her life. The renowned Silla general Kim Yu-shin, with his extraordinary martial arts skills, accidentally saved Princess Tae Ming from an assassination attempt by Mi-seok's confidants and subsequently met Princess Dae Man through her arrangements. While helping Princess Dae Man achieve her grand dream of unifying the three kingdoms, Kim Yu-shin developed feelings for her and became a loyal supporter. With the help of Kim Yu-shin, Princess Dae Man eventually dismantled Mi-seok's influence step by step and ascended to the throne as the first queen of Silla.