Twenty-two years ago, twin brothers Woo-shin and Soo-hyun lost their father in a murder. Woo-ssin, now a successful writer of mystery novels, discovers that his father was murdered with a diamond arrow named 'Adamas'. To get his hands on it, he goes as a ghostwriter to the mansion of Kwon Jae-yoo, the chairman of the Haesong Group, to write his memoirs. Soo-hyun, now a prosecutor, meets Seo-hee, a journalist who wants to find out the truth about the murder from 22 years ago. When Soo-hyun begins to have doubts about his father's death, he reopens the case.