Ella, a girl from the bottom rung of society, was forced to take the place of a missing heiress and get engaged to the fifth son of a chaebol family to save her critically injured brother. But she stumbled into the territory of the family's most dangerous figure, the unhinged second-in-line, Theodore. Amidst pressure and testing, she uncovered a shocking conspiracy lurking behind this impersonation game, one capable of toppling the entire chaebol empire.