(From the publisher):
The planners of the world's greatest engineering feat - the flooding of part of the Sahara desert - knew nothing of the life which teemed below their New Sea. But for the accident which plunged Mark Sunnet and his girl-friend into a cavernous world, nothing would have been known of the catastrophe which now threatened the survivors of the ancient race. Their struggle against doom, and Mark's fight for survival, is the theme of this fascinating story.
Original title: The Secret People
Genre: Fiction→ Science Fiction→ Anthropology/sociology