No man is an island, but Dr. Michael Fisher, a disgraced planetary geologist living on Mars, has never felt more isolated. The situation worsens when both he and Dr. Bex Egunsola, the station's newest biologist, accidentally break through the floor of an unstable lava tube into an ancient subterranean world... and they are not alone.
Is this purgatorial abyss a prison or a sanctuary? Genuine or constructed? How thin runs the line between life and death? And is there a chance for the fallen to return to the world of the living?