Bob Shaw’s 1976 A Wreath of Stars is a stand-alone near-future science fiction. I am ~80% that certain that it was the second Bob Shaw novel I ever read.
Gilbert Snook used his technical skills to travel the world, maintaining aircraft in the breakaway nations so common in the 1990s. It was good life (for him): he made as much money as he needed and he could be as introverted and anti-social as he liked. This worked… until he ended up in the breakaway republic of Barandi. There he pisses off Colonel Freeborn1, second in command to President Ogilvie, and finds himself sent to the diamond mines. Not as a miner, as a teacher, but it’s still not at all the life he wanted.
Then ghosts start appearing in the deepest parts of the mines. If the mines shut down, Snook may be blamed. Indeed, Freeborn will probably enjoy ordering the grating Canadian executed.