Duane decides that the flooded cave is too dangerous to dive into again, forcing the team to explore new access points to the underground cavern system. But something lurking in the darkness forces everyone to reevaluate their safety.

Duane employs ground-penetrating radar to scan the land near a potential drill site, leading to a mysterious finding. Trespassers prompt Charlie to increase security on the ranch with a camera system -- capturing a frightening sight in the dead of night.