Jung I Sin is a serial killer nicknamed “Mantis.” Twenty years ago, she brutally murdered five men. Her son is Cha Su Yeol, who has hated his mother his entire life. He now works as a police officer. One day, a murder occurs. The murder appears to be a crime modeled after Mantis’s. To catch the culprit, Cha Su Yeol asks his mother, Jung I Sin, for help.