The year is 1906. Sixteen-year-old Prudence lives in a New York City tenement with her mother and attends a school where she feels like a misfit. Haunted by memories of her brother's painful dying and by unanswered questions about her father, who never returned from the Spanish-American War, she longs to fight death itself. Prudence takes a job with the health department, where she helps track down the source of a typhoid outbreak, a healthy carrier now remembered as Typhoid Mary. Written as a series of journal entries, the story opens rather bleakly as Prudence writes about her family's poverty, her sense of loss, and her loneliness. But as she discovers a sense of purpose, the narrative becomes increasingly involving and satisfying. In an author's note, Chibbaro comments on her research and her own family history. Occasional line drawings, evidently representing Prudence's sketches, illustrate the text. An absorbing historical novel in which the heroine's professional goals take precedence over matters of the heart.

In 1906, Prudence takes a job at the Department of Health and Sanitation, helping track down the origins of a case of typhoid. Prudence's notes and observation lead to the culprit: "Typhoid Mary." Chibbaro keeps readers deeply engaged in Prudence's perceptions and feelings while delicately spinning out the story's threads, weaving real-life events into her fictional main character's tale.