In 1918, the lives of ordinary Americans are disrupted by two cataclysmic events--an epidemic of influenza and World War I. Lydia Kilkenny is a young woman who works in a Boston department store. She falls in love with Henry Wickett, a sensitive and sickly man who is enrolled in medical school but has little enthusiasm for becoming a doctor. After marriage, Henry drops out of medical school. He tries to enlist in the army but is rejected.

Henry turns his attention to "Wickett’s Remedy"--a tonic accompanied by a handwritten letter emphasizing hope and encouraging recovery. Lydia designs the product’s label and concocts the placebo (based on ingredients revealed to her in a dream). The Remedy is an unsuccessful business venture for the couple.

A businessman named Quentin Driscoll likes the taste, however, and sells the Remedy as a beverage (QD soda). Although Driscoll promises to share future profits from the sale of the soda pop with Henry and Lydia, he fails to honor the agreement. QD soda eventually becomes quite popular, but Lydia never reaps any of the financial gain.

Influenza claims the lives of the two most important men in Lydia’s life--her brother, Michael, and her husband, Henry. She feels helpless and decides to volunteer at the local hospital where she cares for patients with the flu. Lydia realizes that she wants to become a nurse and signs up for a Public Health research project investigating how influenza is transmitted. Unfortunately, none of the test subjects (Navy deserters) contract the flu during the study, but a promising young doctor dies of influenza and pneumonia. Lydia later marries one of the men she meets during the research project.