Bok-soon (Kim Go-eun) runs a street stall while taking care of her younger sister. Bok-soon may not be the brightest girl but what she lacks in intelligence, she makes up for in uncontrollable rage. She's infamously known as the 'psycho bitch' in her neighborhood. Bok-soon's relatively peaceful life with her sister is disrupted when they cross paths with a serial killer named Tae-soo (Lee Min-ki). Tae-soo kills Bok-soon's sister because she may have stumbled upon the truth of his murderous lifestyle. Bok-soon's rage consumes her completely, leading her to plot her revenge on Tae-soo. Meanwhile, Tae-soo vows to tie up his only loose end-Bok-soon. Bok-soon's descent into revenge and electrifying struggle with Tae-soo culminates in a riveting conclusion. Who will emerge alive: hot-blooded Bok-soon or cold-hearted Tae-soo?