A survivor seals themselves inside B-103, a basement bunker in Sillim-dong, Seoul, after an apparent zombie outbreak. Believing they may be humanity’s last survivor, they repeatedly search for radio signals and record video messages for anyone who might someday find them. The zombies never appear directly; their presence is suggested only through sounds, lighting, and the survivor’s fearful reactions.

The bunker contains enough food and water for one year, along with an air purifier, plants, and carefully calculated survival supplies. As the days pass without human contact, however, the survivor’s disciplined routine begins to collapse. They celebrate their birthday alone, talk to objects as though they were companions, and confront fragments of a painful past they have tried to suppress.

When heavy rain floods the bunker, their phone and equipment fail. Food spoils, water runs out, and mold and insects spread through the room. A companion imagined from one of their belongings urges them to leave and return home, but the survivor cannot overcome their fear of the outside world. Even after receiving a Morse-code signal from another possible survivor, they remain unable to open the door.

A year after entering the bunker, the survivor hears someone outside identifying themselves as a census worker. The ordinary voice conflicts with everything they believe about the apocalypse. They briefly prepare to leave but retreat again, convinced that it must be a trap.

As sounds of everyday life continue beyond the reinforced door, uncertainty grows over whether the catastrophe exists outside the bunker or within the survivor’s own perception. They finally put on formal clothes and take up their bag but remain motionless, staring toward a world they still cannot bring themselves to enter.