Cha Young-jin (Kim Seo-hyung) is a relentless detective haunted by the cold case of her best friend, who was murdered 19 years ago by a notorious serial killer. Consumed by guilt and grief, she has dedicated her life to finding the culprit. Nearly two decades later, the killings resurface with a chillingly familiar pattern. Young-jin must now confront her past and hunt down the elusive murderer before another life is lost in this gripping cat-and-mouse chase.