Cage of Souls - Adrian Tchaikovsky
Goodreads
Set in the (presumably) distant future earth where the sun is dying and humanity has pretty much given up about it, it is a story about one man's time in an isolated prison / penal colony, and how he got there. At least so far that's what it has been about.
I really like this author's sci-fi books, but disliked his fantasy books, and this one kinda blurs the edges between the two. So far I've liked it.