Jimin and Taehyung, 19-year-old twins, are just trying to get through college, work a part-time job, and make it home to their struggling family in Goyang. Every evening at 6:30, they take the same quiet train with the same odd mix of passengers - college seniors, grumpy strangers, three rappers, and a couple of loud schoolgirls. Nothing ever changes. Until tonight. A late train. New passengers. No staff in sight. And when the lights go out mid-journey... Something begins to move in the dark. One by one, people start disappearing. And whatever's out there- isn't human anymore. Now trapped in a stalled train, surrounded by strangers, and silence, Jimin and Taehyung must survive the night.

Kim Taehyung, 21, moves to Seoul for his higher education in literature. It's his first time living alone, and the transition from his quiet hometown to the bustling city is jarring. His stepbrother, Kim Seokjin, with whom he shares a strained and distant relationship, arranges a small house for him near the university. It's old, silent, and oddly cheap for the area-but Taehyung, having little choice, moves in. Soon after settling, strange things begin to happen: doors open by themselves, objects move, whispers echo through the halls, and sudden cold spots appear. Taehyung tries to dismiss it all as stress and loneliness, but he can't shake the feeling that something is watching him. One day, trapped inside his bathroom with no way to contact the outside world, a name appears onto the mirror-JIMIN-and he catches his first glimpse of a ghostly figure.