Twin brothers Woosin and Suhyeon lost their father in a murder case twenty-two years ago. Now a best-selling mystery novelist, Woosin finds out that the murder weapon that killed his father is a diamond arrow called "Adamas." In order to get his hands on it, he enters the mansion of Kwon Jaegyu, the Chairman of Haesong Group, as a ghostwriter for his memoir. Suhyeon, now the special prosecutor of the Central District Prosecutor's Office, meets Seohui, a reporter who seeks to reveal the truth of the incident from twenty-two years ago. As he begins to question his father's death, Suhyeon reopens the case.
