Alma, the narrator of Saving the World , discovers a small historical footnote while doing research for a novel: In 1803, a Spanish doctor crossed the Atlantic with twenty-two orphan boys—live carriers of the smallpox vaccine—to inoculate the population of Spain's American colonies. Accompanying them on the two-year voyage was a mysterious woman, Isabel Sendales y Gómez, the rectoress of the orphanage. Captivated by Isabe'’s courage, Alma decides to tell the grueling story of their journey.

Meanwhile, Alma's husband, working with an organization committed to eradicating AIDS in developing countries, travels to the Dominican Republic. When his life is threatened, it is Isabel's strength and resolve that arouse Alma's unexpectedly heroic action.

This novel within a novel presents the radiant stories of two women swept up in campaigns against the scourges of their day.