An impoverished young girl sells herself as a maid to a prince's estate to save her younger siblings. To avoid the covetous eyes of the powerful, she deliberately disguises herself as ugly to hide her beauty, only wanting to work steadily to support her family. By a twist of fate, she is retained by the cold and stern heir, accidentally unearths a harmful evil object, and cures the heir's hidden illness of many years. Seeing through her simple and resilient nature, the heir personally teaches her martial arts and protects her in all matters. With various concubines in the estate harboring hidden currents and successively setting traps to harass and plot against her, she resolves them one by one with wisdom and brute force, and also stumbles upon a deeply hidden family secret of the estate's lineage. The humble maid receives the heir's genuine devotion, and from then on rises step by step, breaking free from the hardships of the bottom tier.