The source of the River Nile was one of the great mysteries of the Victorian age. On an expedition with Richard Burton which reached Lake Tanganyika, Speke went on alone to investigate rumours of the lake he would later name Victoria and proclaim the source of the Nile. This led to a furious dispute with Burton, and it was in the hope of proving his theory correct that Speke launched the expedition that he describes in this book.

One of the great journeys of Victorian exploration, Speke and his companion James Augustus Grant travelled from the island of Zanzibar inland to Lake Victoria and saw the Ripon Falls where the outfall from the lake flows north.