On Karst, the Caves held many secrets and a good living for any man willing to become adapted - a water breather. A select few found it worthwhile, even though it meant they could never leave the planet. Griffith was a loner who went his own way and didn't get involved with the politics of his planet, or with anything or anyone in particular. Until one day he came across a particularly good matrix containing thelemite and found the Colonial Authority and even the Diver's guild after his hide.

Lee Hoffman was active in SF fandom and may be best known for her Westerns - wrote a handful of rather good SF novels. I really like this one, and strongly recommend it. It's the kind of surprise you hand to someone who thinks they've read all the good books.