This is a summary based on our understanding of the series.
Please also note that this summary contains spoilers.
Also known as: Love in the Moonlight
Hong Sam-nom was sold to the palace because of her debt. She became an eunuch (male servant) and served the crown prince. She pretended to be a man. The prince fell in love with her and later on discovered that she is a lady pretending to be a man. Her real name is Hong Ra-on.
She is the daughter of a rebel who organized the riot 10 years ago. She pretended to be a man to protect herself. When she was discovered, she was accused of being the prince’s spy. Despite all that, the prince protected her. When the prince became King, the two of them reunited.