Rourke, a surface dweller, and Evan, the Shelter 17 geneticist who left his underground home, share Rourke's hut now, but their problems are far from over. Rourke wants to include Evan in life at the village, but pressure from other tribal members reopens old wounds Rourke had thought long healed. Tensions build in the tribe as Rourke spirals into depression, and he lashes out at Evan, driving a wedge between them. Evan faces concerns of his own when he discovers dangerous radioactive elements in the water supply. Evan wants to help Rourke, but doesn't know if he can keep their fledgling relationship from collapsing.