Science fiction is a difficult genre to write about. Put in bits of fantasy, and the job becomes tougher.
So I shall commend the author on the attempt, which at least begins well. A group of workers belonging to an oil drilling(?) company and their president are sucked into an underwater volcano/earthquake (the details are pretty hazy), and transferred into a region between the sea bed and the Earth's core, known as Interterra. They discover that the region is inhabited by people who look like them (oh but wait, they are very very good looking, as the characters can't stop thinking about), yet entirely different in their way of living. They reveal themselves as first generation humans, thrive in perfect harmony, and seek carnal pleasure through rubbing of hands (weird much?)
As I write this, I realize the summary is more interesting than the actual content. Oh that's because I missed writing about the central characters. So you have a couple of homophobes, a war veteran (the only bearable character in the book), an oceanographer who's beautiful and compassionate (because she's a woman, duh), and the company President who fleetingly pines for her, before a better product comes along.
Much of the book focuses on unending orgies-all platonic by earth standards, mind you, which only end when the sane character finally broaches the question about their alleged abduction.
When an author thinks, hey let's write something on science fiction, and ends up with this mess, it is only the reader who suffers. The book receives an additional star of the final twist in the story.
P.S. Jules Verne did a far better job of writing books on this genre (and somewhat similar plotline), more than a century ago. Creative imagination needs talent, hence proved.