Eulji Hae Yi is a ruthless lawyer who wins all of her cases. She goes to meet with Jang Hwa Sa, a death-row convict who is the infamous killer behind a poison murder case. Inside Room No. 9 of the high-security women’s prison, the souls of Hae Yi and Hwa Sa change bodies. Doctor Gi Yoo Jin, Hae Yi’s boyfriend, somehow hold the key to the two women’s fate.