"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, grows up to become the first queen of Silla - Queen Seondeok.
In the situation where Mi-Shil (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, giving birth to twins is considered extremely unlucky, with the omen "Seong-gul nam-jin" (the sacred bone will be followed by men). Out of necessity, King Jinpyeong sent someone to send away the second daughter, Dae-Man, but Mi-Shil secretly sent people to pursue and kill her. At a critical moment, Dae-Man was saved by the legendary Hwarang figure, Moon-Nu, who devised a plan and handed her over to Cho-Hwa, a servant of King Jinpyeong, to raise. Cho-Hwa took Dae-Man to the desert regions of China and raised her in a small inn. Mi-Shil, Dae-Man's greatest enemy, used her outstanding beauty as a weapon to gain the favor of King Jinheung and thus wielded power in the palace. Filled with ambition, after King Jinheung's death, she supported the young King Jinpyeong's ascension to the throne. After the wife of King Jinpyeong gave birth to twin daughters, Mi-Shil planned to use the lives of these twin daughters to threaten him and directly seize royal power. Unexpectedly, Moon-Nu and Cho-Hwa saved Dae-Man, disrupting her plans. Mi-Shil, who held great power, did not abandon her struggle for the throne and plotted to have her husband ascend the throne, viewing Dae-Man's twin sister, Princess Cheonmyeong (played by Park Yi-Jin), as a thorn in her side. Under Mi-Shil's control, Princess Cheonmyeong, with her extraordinary wisdom and quick judgment, did not easily reveal her true nature but always demonstrated the leadership abilities of a princess at critical moments. Although Princess Cheonmyeong married Gim Yongsu (played by Park Jung-Cheol) and had a son, Gim Chunju (played by Yoo Seung-Ho), she developed feelings for Gim Yu-Sin (played by Yeom Jae-Hyeong), who had once saved her life. The renowned Silla general, Gim Yu-Sin, with his extraordinary martial arts skills, accidentally saved Princess Cheonmyeong from an assassination attempt by Mi-Shil's confidants. Arranged by Princess Cheonmyeong, he met Dae-Man. While helping Princess Dae-Man realize her grand dream of unifying the three kingdoms, he developed feelings for Dae-Man and became her loyal supporter. With the help of Gim Yu-Sin, Princess Dae-Man gradually dismantled Mi-Shil's forces and ascended to the throne as the first queen of Silla.