A baby is found abandoned inside a coin locker at Western Seoul train station in 1996. A beggar takes her and names her Il-young (Kim Go-eun), then when she turns 10, she is taken by the corrupt detective who sells her off to a woman referred to simply as Mother (Kim Hye-soo) as part of his loan payment. Mother is the boss of a loan shark and organ trafficking crime ring in Chinatown, Incheon; she has held on to her position of power by being dispassionate and calculating, and by keeping by her side only those of use to her. Mother decides to raise the young child after she shows toughness and smarts, eventually grooming her for a position in her organization as her personal debt collector. One day, Il-young is given a task to collect debt from Suk-hyun (Park Bo-gum), the son of a debtor. Over the course of a few days, she is initially taken aback by the guy, who doesn't seem afraid of her and even shows her kindness and openness when talking about his own struggles, before starting to develop feelings for him. But when his father flees from the debt, Mother orders her to kill Suk-hyun, an order Il-young fails to follow. Regardless, Suk-hyun is killed and organ-harvested by Mother's other goons. Il-young is beaten down and readied to be shipped for Japanese flesh trade. The only family she has ever known comes crashing down. Il-young escapes and makes her way back to Mother, and kills her, only to find out that she is actually her birth mother and that her mother uses this opportunity to teach her a lesson and train and prepare her for taking over.
