Geo-Wool (Kyung Soo-Jin) lives with her family members, including her younger brother Du-On (Lee Ji-Hoon). She is single and very noisy. She takes care of all the complaints made by her neighbors. Her relationship with her brother is rocky, as they don't get along. One day, they have an argument and she decides to become independent. She moves into Baekse Apartment by herself. On the first night in her new home, she hears noises at 4 AM that come through the floors. She can't sleep due to the unknown noise. Geo-Wool and her neighbors look into the secret surrounding the noise that comes through the floors.