The series begins with a gruesome murder in a prison, where a death-row inmate kills multiple prisoners and a guard. This event rekindles the national debate on the death penalty in South Korea.

One month later, we are introduced to twin brothers:

Ha Woo-shin: a famous mystery novelist

Song Soo-hyun: a dedicated prosecutor

Their lives take a turn when they begin to uncover strange clues related to their father's death 22 years ago.