Roger Zelazny wrote SF, but quite a few of his stories were of the mystery/thriller variety, including "The Eve of RUMOKO." I've read this one a couple of times, first in a collection titled My Name is Legion, and this time in The Mammoth Book of New World Science Fiction: Short Novels of the 1960s. My theory is that you can't go wrong by re-reading any of Zelzany's early work.
This story (or novella) is about an unnamed narrator (he calls himself Albert Schweitzer) who works as a free-lance espionage agent, or something similar. This time he's on a ship with quite a mission: it's going to place atomic charges and create a volcanic island -- living space on an over-crowded planet. His job is to prevent sabotage, which he does, but things don't necessarily work out to his liking. There's betrayal, of course, which is always good in an espionage tale, and the ending's much darker than you might have expected when you started reading.
Zelazny had a way with words. I admire many of his novels and shorter works, and while this may not be the best of them, it's certainly worth checking out.