The Secret People
John Wyndham
 The Sahara is being flooded to create a new sea when the protagonist of the novel, Mark Sunnet, crashes his private rocket plane into an island of what is currently little more than a large lake. He soon finds himself and his female companion sucked into an underground cavern where they are promptly captured by mysterious pygmies. The diet of little people is centred around large fungi; the captives speculate that stories which reached the surface of the little people and their giant mushrooms may have led to the myth of gnomes. Sunnet finds that a tiered community has evolved in the underground caverns - the pygmies inhabiting a large underground collection of natural and artificial caverns and tunnels, and the captured humans in a deliberately isolated subsection of the caverns. He is also surprised to learn that family life exists in the caverns - "natives", children of captured humans who were born and have lived all their lives in the caverns exist, and are generally happy with their life, and have no wish to escape. Most of the captured humans do wish to escape, and two different methods are being tried. Both are tunnels, one going up at an angle, to try and break through to the surface, and another on a level, hoping to intersect a pygmy tunnel or cavern, from where they will be able to make their way to the surface. The pygmies are distressed, and it is Sunnet's arrival that reveals why to the captives - the pygmies fear their environment will be flooded and destroyed by the newly formed Saharan Sea. Their fear is well founded, and the waters break through into the pygmy caverns, eventually flooding the entire ecosystem. Sunnet and a handful of others survive, and finish the story being sunburned after years of subterranean life, and establishing a new company based on primitive - but unique - technology they rescued from the caverns.