Two best friends transmigrate across worlds to become twin sisters, sent by an enemy nation as spies to marry Prince Rui, the cold elder brother, and Prince Jing, the cunning younger brother. The two princes suspect the twins and plot to kill them. However, the elder sister, whom her brother sees as a 'master spy,' is actually a pure girl obsessed with studying, clueless about love or schemes. Meanwhile, the younger sister, whom her brother perceives as 'innocent,' is a heart-fluttering temptress, so manipulative that even her brother is defeated. A chaotic romance filled with misunderstandings begins.