University student Toru heads to the mountain ski pension Spool in Nagano with his girlfriend Mari, hoping the trip will bring them closer. The pension fills up with guests during a blizzard: part-timers Toshio Kubota and Midori Shinozaki, three office workers named Kanako, Aki, and Keiko, a Kansai boss and his wife Kayama, freelance photographer Yosuke Mikimoto, and a sunglasses-wearing man named Ichiro Tanaka who keeps conspicuously to himself.
After dinner, a note appears in the office workers' room: Tonight at midnight, someone will die. It is dismissed as a bad joke. Before nine o'clock, the sound of breaking glass draws people upstairs—where Tanaka's room holds a dismembered body, an open broken window, and no sign of the killer. The blizzard has cut off the roads and phone lines, sealing everyone inside. With the police unreachable and a murderer still among them, the survivors must identify the killer before more bodies appear.