What is the main idea?

Daniel Defoe's A Journal of the Plague Year is a first-person, mostly nonlinear narrative told by protagonist H.F., an unmarried saddler whose name is only revealed by his signature at the end of the work. The Journal is a tale of his experiences during the plague that afflicted London in 1665; the work is thus fiction but is peppered with statistics, data, charts, and government documents. H.F. begins by relating rumors that the plague had come to Holland, and closely follows the bills of mortality.