该剧根据药丸岳小说《恶党》改编，讲述侦探社佐伯修一在年幼时，姐姐惨遭杀害。他在经手几件凶杀案之后，开始调查当年姐姐被杀害的案件。

Saeki Shuichi was a detective, but he quit his job. He now works at a detective agency. One day, a couple asks the detective agency to find a man named Sakagami. The man killed the couple's son and served at a youth detention center. Kogure Masato is the director of the detective agency. He tells Shuichi to work on the case. Shuichi is also part of a victim's family. When he was a child, his older sister was murdered. While Shuichi watches Sakagami, the couple asks him to find some materials which will allow them to forgive Sakagami or not.

어린 시절 누나가 살해당한 전직 형사이자 탐정인 그가 출소한 범죄 가해자를 조사하며 벌어지는 이야기를 그린 서스펜스 드라마