Starfish is the first of a trilogy, and I accidentally read the second book in the series already, Maelstrom, which I talk about here.
Here is the basics of Starfish.
A huge international corporation has developed a facility along the Juan de Fuca Ridge at the bottom of the Pacific Ocean to exploit geothermal power. They send a bio-engineered crew–people who have been altered to withstand the pressure and breathe the seawater–down to live and work in this weird, fertile undersea darkness.
Unfortunately the only people suitable for long-term employment in these experimental power stations are crazy, some of them in unpleasant ways. How many of them can survive, or will be allowed to survive, while worldwide disaster approaches from below?
Really fine, really really fine.