The disappearance of a master key from an aging Tokyo apartment complex triggers a cascade of paranoia and the eventual discovery of a child's remains in the basement. The narrative follows the interconnected lives of the elderly female residents who navigate the claustrophobic confines of their shared living space. As the investigation unfolds, the residents must confront long-buried secrets and the fragility of their social order. The story utilizes a multi-perspective framework to examine the tension between the residents and the external forces threatening their precarious stability.

Readers and critics frequently note the precise, clinical prose style that heightens the sense of unease throughout the narrative. Discussion often centers on the author's ability to transform a mundane apartment building into a site of profound psychological tension. Many observers highlight the effective use of the setting to mirror the internal states of the characters. The pacing is described as deliberate, favoring character-driven revelations over rapid-fire action sequences. This work is often cited for its contribution to the subgenre of Japanese domestic mystery.