Andromeda: The Sojourn: Hard Science Fiction (The Long Journey)

Nova is a lonely planet, on its way to the Andromeda galaxy for ages. And yet it is inhabited - by people who have never known anything other than the caves beneath the surface that protect them from the vacuum and cosmic radiation.

A surprising encounter changes everything. The planet gets visitors who seem to have their own agenda and are so alien that communication seems futile. But they, too, have unexpected existential problems. Could cooperation with them avert the danger of missing Andromeda? Perhaps, were it not for a threat that has lain dormant inside the planet for millions of years and could destroy all life.