This felt at first more like fantasy than science-fiction. The characters are living in a planet without a sun, made inhabitable by geothermal activity and life, a lot of which generates the only light available to this people, the incestuous descendants of a couple from Earth marooned in this strange world five generations ago and quickly devolved to a stone-age state and a culture that shackles them with a sort of cargo-cult ritual and passivity and may condemn them to starvation. The shadow of their astronaut ancestors and their 'three companions' looms large, as is the hope of rescue by Earth. I found the story gripping, the characters very believable if not always easy to like and was sorry to reach the last page. I liked it enough that I hope there'll be a follow up (which I suspect there'll be, as there are loose ends in the story that would need tying up).
Link to the book on Amazon here.
The author's web site: http://www.chris-beckett.com