Although the narrative begins and ends in San Francisco and offers an intervening excursion to New York City, most of the action takes place on Krakatoa, a volcanic island west of Java in the Pacific Ocean. The year is 1883.

The events of the plot are defined by the volcanic setting in many ways. An ominous rumbling permeates the land as the ground constantly shifts and settles. Because of the quivering landscape, people must acquire "mountain legs" to walk steadily, just as a sailor needs "sea legs." Krakatoa also boasts several rich diamond mines that keep the first settlers on the island in spite of the dangers.

In addition to a dramatic, towering volcano, du Bois's Krakatoa also offers many technological wonders, including the House of Marvels, a museum filled with wildly imaginative inventions such as a bed-making machine; and a balloon merry-go-round, consisting of seven boats joined together...