Yujia, a successful career woman at a large corporation, is a workaholic who feels that her life is empty at the age of thirty. This is because her closest friend from high school, Somin, was murdered by the teacher she had a crush on, Im Dayun. One day, Yujia meets someone who will become her brother-in-law through her older sister, Jiyoung. He is Jaehyun, her teacher from high school. The reunion with Jaehyun brings back memories of Somin that Yujia had tried to forget, and as those memories become clearer, she finds herself in anguish. After spending days filled with confusion and pain, Yujia learns from Jaehyun that the release date of the murderer Dayun is approaching. Determined to uncover the truth behind the incident, Yujia gathers her courage to meet Dayun. However, before she can meet Dayun, she hears the news of Dayun's suicide and, feeling lost, goes to the funeral home. In the cold funeral home with no mourners, Yujia meets Dayun's younger sister, who reveals a shocking story: Dayun is not the true culprit. Although Yujia doubts the truth of her words, a foreboding feeling leads her to decide to attend the reunion, wondering if there might be hidden truths. A few days later, at the reunion, Yujia unexpectedly hears from her classmate Eunyeong that Somin had a crush on a girl her age and had sought counseling from Dayun for that reason. Shocked that she was unaware of her closest friend's struggles, Yujia gets into a car accident on her way home.