The Eunuch's Secret summary: Yu Hari and her brother, Yu Hahyeon, care for their ailing family. Their situation takes a turn for the worse when their uncle, to whom they owe a debt, decides to send Yu Hahyeon to serve as an eunuch in the palace of Prince Sohyeong. In a desperate attempt to protect her brother, Yu Hari makes the difficult decision to go in his place. What seemed like a simple task becomes complicated when the prince discovers her true identity. Trapped inside the palace, Hari must find a way to survive. Will she be able to do it?