What if the eldest daughter-in-law who was condemned at the in-laws is a psychopath? This is a resort where the legend of man-eating demons called the Devil’s Cave comes down. Ji-ae, who had a happy time with her husband, was managing a lodge pension. In an accident with her husband who went swimming in the valley, she became a widow after falling asleep. A sister-in-law demonstration who heard of the obituary of an unexpected brother. He goes to the lodge with his fiancé, Sky. That’s how the three people lived together.
One day, Min-sang who is not that handsome becomes a huge success because of a webtoon. Then he gets a pretty wife, Yu-ra, for himself. Min-sang is having a dream-like marriage with Yura. It has been a perfect day except for his sister-in-law Yu-mi, who hates her ugly self. Accidentally, he learned of his wife's dark past through his sister-in-law's diary, and this leads to a reversal of the relationship with her sister-in-law. Min-sang began to demand excessive demands from his sister-in-law, and Yu-mi began to accept them. Where will the end of the relationship between Min-sang, Yu-ra, and Yu-mi lead?