A drama about Kim Cheo Seon's life during the Joseon Dynasty. Kim Cheo Seon was a loyal and faithful eunuch for various Kings, such as the 5th King, Munjong, and the 10th King, Yeonsangun, during the Joseon era.

In the Joseon Dynasty period, the kingdom was enveloped in a political maelstrom. Cheo Seon was born as a posthumous child and separated from his mother immediately. He was raised by Weol Hwa and the old Swe Gwi, who ran the eunuch school. When he meets So Hwa, the daughter of a powerful noble, he falls in love with her immediately. He voluntarily becomes a eunuch to be close to So Hwa and is assigned to work for Cho Chi Gyeom, a senior eunuch. Entering the royal palace, he sees King Sung Jong and So Hwa spend their first night together. He becomes So Hwa's loyal protector.

As the political battles rage on among the courtesans and wives in the palace, So Hwa is chosen by the king to be his queen and Cheo Seon vows to be her loyal servant. But So Hwa is eventually dethroned as the queen and leaves the palace in disgrace. Cheo Seon helplessly watches these events unfold and he secretly helps So Hwa. But in a cruel twist of fate, he is the one chosen to execute So Hwa's death sentence by serving her a bowlful of poison. After So Hwa dies, he looks after her son King Yeon San as if he were his own son.