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 is a former investigator working at a detective agency when his boss assigns him a case requiring surveillance and monitoring of a murderer who has served jail time for killing a man. The murdered man's parents are investigating whether the criminal has reformed or not. Shuichi feels a personal connection to the case.