The Secret People

While flying over Africa's New Sea, a water project in the heart of the Sahara desert, Mark Sunnet's rocket plane crashes and is sucked through a hole in the desert floor into a strange, cavernous new world.

There, he and his partner Margaret encounter the survivors of an ancient race of underground dwellers whose whole existence is now threatened. Captured and forced to live with other prisoners taken from the surface, the pair know that they must escape before the waters above drown them all . . .