Nothing is more frightening, as the narrator points out, than a ‘time-rich nosy person’. Exhibit A is Ahn Geo-ul, who commits herself to social justice causes with terrifying tenacity. After temporarily renting a unit in the Baek-sae Apartment building, she discovers that a loud, hard to locate banging noise occurs from 4am every night, making the residents’ lives an insomniac hell – and so she determines to engage in her own disruption and to find the culprit of this acoustic assault, simultaneously eliminating her eccentric neighbours as suspects, and recruiting them to her cause.