From the publisher:
The early 1920s saw the first, small commercial airlines. The aircraft, often flying boats, are sturdy and easily patched up but have few instruments for navigation. Flying is an art, not a science. This is especially so in the still-wild regions of the Dark Continent, Africa.
Darkest of all is the wilderness of Belgian Congo, in the very center of the continent. Belgian colonial rule is very harsh, and traditional practices such as slavery and witchcraft remain rampant. The few airmen who offer their services in such a place are veterans of the Great War. They navigate Central Africa by following the wide, dark, Congo River, but when night falls the only place to land is on the river itself. And there, in the African continent’s true heart of darkness, little has changed in the twenty years since Joseph Conrad wrote his well-known book on the hell-hole that is Belgian Congo. Superstitions rule the tribes that live on or near the river. The greed of the Belgian colonial administration, for ivory, rubber, and copper, surpasses even that of the Zanzibari slavers, feared for their raids among the Congo natives.
But the Dark Continent hides secrets as well. In deepest Congo, a treasure-house from primeval times awaits those who dare seek it out and survive the search. An ancient flying city known as Devapura, built by an unknown civilization, and last recorded in an ancient manuscript seen in the early eighteenth century by Jonathan Swift, who copied the details into a fictitious story about one Lemuel Gulliver, who reportedly saw the city flying in July 1707. Grounded in the heart of Africa for millennia and now inhabited by nameless horrors, will Devapura again rise into the sky?
This monograph consists of a series of linked adventures that bring the investigators on a flying expedition across the Atlantic and along the Congo River into the very heart of the Dark Continent. They race against time, since a rival expedition, led by a sinister, wealthy industrialist bent upon summoning Great Cthulhu himself, already seeks for the ruins of Devapura and the secrets hidden there. But the investigators have one ace up the sleeve: their Curtiss F-5L flying boat can move faster than any river steamer. But only in daytime, and only if they survive the cannibals and other sundry dangers that strike at night.