After their school bus breaks down in the middle of a dead desert road, Eun-bi and her classmates discover a mysterious luxury building standing alone in the heat. Inside, the food is warm, the halls are silent, and something feels terribly wrong. Then the doors disappear. The road vanishes. And the entire building is suddenly trapped in the middle of a violent endless sea. As strange rules begin appearing on their phones, students start disappearing one by one. Shadows move through the hallways after midnight, the dead refuse to stay dead, and Eun-bi realizes someone inside the building was never human to begin with. To survive, they must uncover the truth behind the cursed Red Stone, the haunted house, and the horrifying secret their class buried long ago. Because this building doesn't just trap people. It judges them.