The One-Eyed Man by L.E. Modesitt Jr.
When offered a job on Stittara, Dr. Paulo Verano (a freelance ecological consultant) accepts, looking for a new start after difficulties in his personal life. The planet is a main producer of anagathics, drugs which can double the human life span. He soon gets caught in the political pressures of the government as uninterrupted flow of the longevity drug is top priority to the officials, even to the destruction of the human settlements.
Verano discovers wonders and mysteries on Stittara, such as the giant sky tubes which drift in the skies of the planet whose nature is unknown and may be linked with the destructive electrical storms that drive the inhabitants of the planet to live below ground. Ancient settlements linked to the planet's ecology, outland settlers who manage to live in harmony with the land, a woman who may be over 400 years old, and secret agendas the government is trying to cover up all combine to keep Verano racing for answers.