Shadow Detective follows Kim Taek-rok, a veteran detective nearing retirement who suddenly finds himself framed for a murder he did not commit. A mysterious blackmailer calling himself 'Friend' begins putting Taek-rok through a series of dangerous games, forcing him to dig into his own past cases and investigate the corrupt elements within his own police department to clear his name. As the mystery deepens, Taek-rok is joined by dedicated new colleagues who help him navigate the treacherous web of conspiracy. The second season escalates the tension as he continues his relentless pursuit of the mastermind known as 'Friend', uncovering a vast criminal syndicate that reaches the highest levels of power and threatening the lives of everyone he holds dear.