A financial arrangement regarding a Parisian apartment transforms into a psychological obsession for Monsieur Baudoin. Baudoin enters into a life annuity contract with Madame Vallette, securing the rights to her property upon her eventual demise. Driven by a morbid interest in the timeline of his investment, he begins to track her daily movements and health status with increasing intensity. The narrative explores the tension between his desire for the asset and the reality of the human life standing in his way, maintaining a focus on his internal fixation.

Readers often note the clinical precision with which the author depicts the protagonist's descent into obsessive behavior. Discussion frequently centers on the ethical implications of the contract and how it warps the relationship between neighbors. Critics highlight the atmospheric portrayal of Paris as a backdrop for the protagonist's increasingly erratic monitoring. The narrative is frequently described as a slow-burn study of human avarice that avoids sensationalism in favor of psychological realism.