During a family trip at a secluded pension, Eunchae sneaks into the room of Seunghyun, her long-time crush, to steal a bold kiss. However, the man who responds fiercely in the pitch black is not Seunghyun, but her arch-nemesis, Kang Taeyun! 'Why? Are you upset it’s not him? Don’t worry. I’m better.' Following this fatal mistake, Taeyun seizes Eunchae's weakness and proposes a provocative one-month bet involving a 'leash.' Will Eunchae be able to win this dangerous game and reclaim her pride, or is she walking straight into a trap he meticulously designed?