Mary Mallon came to New York from Ireland as a teenager in 1884 and, like so many immigrants, found work as a domestic servant in the houses of well-off families. She became known as a talented cook and worked for a number of wealthy clients. Unfortunately, one or more people in her employers' houses invariably came down with typhoid, a fever caused by bacteria in feces. Mary, who was later described as not very fastidious about hand-washing, spread the disease by handling food.

One of the stricken families hired Dr. George Soper, a sanitary engineer, to investigate the source of the illness. He subscribed to the fairly new germ theory of disease; previously, contagious illness was thought to emanate from the filthy air given off by garbage and was associated with poverty and dirty living conditions. In 1907, he found that the only constant among the patients was their cook, Mary Mallon, soon to be dubbed by journalists as "Typhoid Mary." She had the dubious distinction of being the first healthy carrier of the disease discovered in the United States.

Although she had not committed a crime, she was tried, found guilty and sent into a three-year quarantine. Given back her freedom on the condition she never cook professionally again, she broke that promise, caused a new outbreak while cooking in Sloane Maternity Hospital from 1910 to 1915, and was sent back to North Brother Island in the East River till her death in 1938.

"Fever" (Scribner, 306 pages, $26), Mary Beth Keane's novelization of her life, is fluent and confident and adheres to the true events. She presents Mary as a stubborn, proud but likable woman. (The real Mary, given to outbreaks of rage and an irrational hatred of doctors, seems a good deal less personable.) In life and novel, Mary refuses to believe she's at fault for at least 51 illnesses and three deaths; it's understandable that germ theory would sound outlandish to her.

Keane does a fine job of conveying the textures of Mary's daily life as an overworked, underpaid laborer. (In the laundress job she tries for some years, she must wrestle with heavy damp fabric for 6½ days a week.) Her salary pays only for a bed in an apartment shared with other people.

The real Mary Mallon had no family, but Keane gives her a live-in partner named Alfred, a German immigrant. For most of the novel, he provides a counterpoint to her resilience and fortitude, a man who keeps losing jobs because of his drinking. After a terrible accident, he is prescribed morphine, cocaine and heroin for his pain, a practice common at the time. Not surprisingly, he becomes addicted and even less employable.

What I was unprepared for was Keane's decision, in the last third of the novel, to adopt Alfred's point of view in alternation with Mary's. Alfred is rather a cipher. Promoting his status feels like a structural mistake, or padding, given Mary's liveliness and intelligence. But even if you aren't interested in the medical detective story, you'll enjoy the rich portrayal of work and class divisions at the turn of the 20th century.

Brigitte Frase is a book critic in Minneapolis.