In a quiet town in Korea, 18-year-old Park Stella needs help with her grades, so her mom hires a tutor named Kim Taehyung. But Taehyung has a dark and twisted secret-he hates girls and kills every student he tutors after a week. As Stella begins her lessons, Taehyung starts to feel something he never expected-he's falling in love with her. His dark urges become harder to control, and Stella starts to sense the danger. She must discover the terrible truth and escape before she becomes his next victim.

When Elena is kidnapped on the night before her wedding, her younger sister Y/N is forced to marry her fiancé, Kim Taehyung, in her place. Taehyung resents Y/N, making her life a constant struggle. Just when Y/N begins to uncover the truth behind Elena's disappearance, Elena returns. But instead of a joyful reunion, Elena harbors hatred towards Y/N for marrying Taehyung.