Starfish - Peter Watts

Civilization rests on the backs of its outcasts.

So when civilization needs someone to run generating stations three kilometers below the surface of the Pacific, it seeks out a special sort of person for its rifters program. It recruits those whose histories have preadapted them to dangerous environments, people so used to broken bodies and chronic stress that life on the edge of an undersea volcano would actually be a step-up. Nobody worries too much about job satisfaction; if you haven't spent a lifetime learning the futility of fighting back, you wouldn't be a rifter in the first place. It's a small price to keep the lights going, back on shore.

But there are things among the cliffs and trenches of the Juan de Fuca Ridge that no one expected to find, and enough pressure can forge the most obedient career-victim into something made of iron. At first, not even the rifters know what they have in them - and by the time anyone else finds out, the outcast and the downtrodden have their hands on a kill switch for the whole damn planet...