Hae-joon (Park Hae-il), who is investigating a murder case in the mountains, meets Seo-rae (Tang Wei), the wife of the deceased. "I was worried that he hadn't returned from the mountains, thinking that he might have died after all." Seo-rae shows no signs of excitement about her husband's death, and her behavior is so different from that of grieving relatives that the police believe she is the suspect. As Hae-joon interrogates and monitors Seo-rae, he realizes that he is gradually becoming interested in her. Meanwhile, Seo-rae begins to take bold actions against Hae-joon despite being accused of a crime. A suspect who hides the truth. A detective who wants to suspect the suspect at the same time. They have a decision to break up.