The narrative follows the life of Mary Mallon, a cook in early 20th-century New York, whose asymptomatic status as a typhoid carrier leads to her forced isolation and societal ostracization. Federspiel explores the collision between individual liberty and public health mandates through the perspective of a woman labeled a public menace. The protagonist navigates a world defined by rigid class structures, early germ theory, and the bureaucratic machinery of the New York City health department. The narrative framework utilizes a blend of historical reconstruction and psychological interiority to examine the isolation of the titular character. The primary opposition manifests as the medical establishment and the public fear surrounding the spread of disease.

Discussion often centers on the author's ability to humanize a figure frequently reduced to a medical footnote in history. Readers frequently highlight the stark, atmospheric quality of the prose, which effectively conveys the claustrophobia of the protagonist's experience. Critics often note the balance between historical accuracy and the imaginative reconstruction of Mary's internal life. The narrative is frequently cited for its cold, objective tone, which forces readers to confront the complexities of the moral dilemmas presented. Many find the exploration of the power imbalance between the state and the individual to be the most compelling aspect of the work.