Eul Ji Hae Yi is a ruthless lawyer who wins all of her cases. She goes to meet with Jang Hwa Sa, who is on death row for an infamous case of poisoning serial murders. Inside Room No. 9 of the high-security women’s prison, the souls of Hae Yi and Hwa Sa change bodies. Does psychiatrist Gi Yoo Jin, who is Hae Yi’s boyfriend, somehow hold the key to the women returning to their own bodies?