Sister.

Desperate to raise money for her younger sister's surgery, Hae-ran teams up with Tae-soo to kidnap her half-sister So-jin. So-jin wakes up confined in an unfamiliar place. Hae-ran and Tae-soo demand a hefty ransom, expecting her wealthy father to cough up the money. Upon discovering that one of her captors is her half-sister, So-jin enters a precarious alliance that blurs the lines between victim and perpetrator as she plots a counterattack against the ruthless Tae-soo.