Criminal profiler Kang Tae Joo is pulled out of retirement by a chilling summons: an imprisoned serial killer has been linked to additional unsolved deaths through DNA evidence, but he insists that Tae Joo joins the investigation, believing that Tae Joo can prove his innocence. Tae Joo is brought back into a world he thought he'd left behind 33 years earlier, forcing him to face ambitious prosecutor Cha Si Young, with whom he shares a difficult past, in pursuit of the truth. But as with many cold cases, the truth isn't as straightforward as it seems – and Tae Joo might be more involved than even he knows. Can Tae Joo finally close the chapter on the "Scarecrow" murders for good, or will a new twist upend his life?