In a small village in South Korea, a young woman named Seo-yeon receives a mysterious phone call that will change her life forever. The voice on the other end belongs to Young-sook, a woman living in the same house but 20 years in the past. At first, Seo-yeon tries to understand how this is possible, but soon realizes they have the opportunity to talk and help each other improve their lives. Over time, their friendship blossoms through the phone lines, and the two women share secrets, dreams, and desires.
However, as they delve further into each other's lives and decisions, things begin to take a dark turn when Young-sook, influenced by Seo-yeonโs warnings, makes choices that lead her down a shadowy path. The line between good and evil quickly blurs, and in an unexpected twist, Seo-yeon realizes that her actions have devastating consequences in the future.
With a sense of urgency and rising tension, Seo-yeon embarks on a mission to undo the effects of their interactions. The film transforms into a psychological thriller as it explores themes of guilt, fate, and the complex nature of time. In a life-and-death game that transcends time barriers, Seo-yeon must find a solution before itโs too late, for both herself and Young-sook.