A scholar and explorer, Dr. Samuel Fergusson, accompanied by his manservant
Joe and his friend professional hunter Richard "Dick" Kennedy, sets out to
travel across the African continent — still not fully explored — with the help
of a hot-air balloon filled with hydrogen. He has invented a mechanism that, by
eliminating the need to release gas or throw ballast overboard to control his
altitude, allows very long trips to be taken. This voyage is meant to link
together the voyages of Sir Richard Burton and John Hanning Speke in East
Africa with those of Heinrich Barth in the regions of the Sahara and Chad. The
trip begins in Zanzibar on the east coast, and passes across Lake Victoria,
Lake Chad, Agadez, Timbuktu, Djenné and Ségou to St Louis in modern day Senegal
on the west coast. The book describes the unknown interior of Africa near
modern day Central African Republic as a desert, when it is actually savanna.