Reborn back to twenty minutes before the tragedy occurs, inside the girls' dormitory, the protagonist clearly knows that at 11:40 someone will knock on the door under the pretext of a sudden room inspection. Once the door is opened, all four people in the dorm will perish. She hurriedly persuades her roommates to barricade the door. The roommates are half-doubting, worried about receiving a demerit that would affect their graduation. Time ticks closer second by second, and the knocking for the room inspection sounds outside the door right on time. Everyone demands that the other party verify their identity. Danger is right outside the door, and a dormitory survival standoff officially begins.