Stittara is the primary source of anagathics: drugs that have more than doubled the human life span. But the ecological balance that makes anagathics possible on Stittara is fragile, and the Unity government has a vital interest in making sure the flow of longevity drugs remains uninterrupted, even if it means uprooting the human settlements. Offered the job of assessing the ecological impact of the human presence on Stittara, Dr. Paulo Verano gets far more than he bargained for: Stittara's atmosphere is populated with skytubes-mysterious airborne organisms that drift like clouds above the planet. They've eluded humanity for centuries, but Verano believes his conclusions about Stittara may hinge on understanding the skytubes-if he survives his investigation.