The El Dorado Adventure, like all the Vesper Holly books, is set during the Victorian era, either in the United States, in an imaginary country, or in both. The Victorian setting is important because Vesper is not a stereotypical young lady of the period. Her adventures and her behavior are directly opposed to those expected of a wellbrought-up young lady from Philadelphia.

The action in The El Dorado Adventure, which takes place in 1872, begins at the Holly estate in Strafford, Pennsylvania, near Philadelphia, and quickly moves to the imaginary El Dorado, a country similar to Panama, in Central America. At the beginning of the story, Vesper learns that she has inherited property near Puerto Palmas, a river port in El Dorado. Intrigued by the idea of owning a volcano, Vesper convinces her guardian Brinnie that he needs a relaxing ocean voyage to Central America. Although the voyage is...