Addiction: The Lady Upstairs: A newlywed couple moved to a new house with big dreams. However, it was Hong-yeon, the landlord of Saek-gwang who was waiting for them. A strange atmosphere flows between Hong-yeon, who secretly seduces Jeong-woo, Jeong-woo, who is struggling not to fall for it, Yoon-gi, a slave man wearing a husband's mask, and Yoon-mi, who knows nothing. Will Jeong-woo be able to protect his family amid the endless temptation of the landlord?