Bok-Soon (played by Kim Go-eun-I) operates a street food stall while also looking after her younger sister. Although she may not be the sharpest, her intense and uncontrollable anger compensates for her lack of intelligence. In her neighborhood, she is notoriously referred to as the “psycho bitch.” Her relatively calm existence with her sister is shattered when they encounter a serial killer named Tae-Soo (portrayed by Lee Min-ki). Tae-Soo murders Bok-Soon’s sister after she inadvertently uncovers his deadly secret. Overwhelmed by fury, Bok-Soon becomes consumed with the desire for vengeance against Tae-Soo.