At the request of the Denobulan Science Academy, Enterprise goes to rescue a group of three geologists from a planet now being controlled by a group of xenophobic militants who decree that all off-worlders must evacuate. Being experienced with caving, Ensign Mayweather is chosen to lead Commander Tucker and Lt. Reed on the rescue mission underground. They have only three days to return to the surface with the scientists before the negotiated government ceasefire expires.
As the Enterprise nears the planet, it comes to the aid of an alien transport, suffering from a dangerous radiation leak, which is denied permission to land. The most seriously injured of the various aliens brought aboard is Hudak, an Antaran, whose species has a centuries long history of conflict and animosity with the Denobulans. Though suffering from a fatal case of radiation poisoning, and being the first time the divorced species have interacted in generations, he immediately refuses help from Dr. Phlox. Archer orders Phlox to treat him, but he reluctantly declines, since Denobulan medical ethics places the patient's wishes above all other considerations.
Underground, the crew make good progress, but Mayweather injures his leg while saving Reed who missteps and drags Tucker down an abyss. Leaving Mayweather behind, Reed and Tucker soon find the Denobulan geologists who are happily engaged in recording the various rare and precious geological features of the cavern. With time is running out, Tucker is insistent the group departs, but the scientists downplay the threat imposed to them. Tucker himself insists that his orders need to be fulfilled, and the geologists soon prepare to head to safety.
Back on the ship, using tact and diplomacy of his own, Phlox endeavors to try to help Hudak, but his initial attempts end in failure. Phlox, for his part, is also upset at the mutual hatred between the two species, particularly given that it is a long standing source of tension between him and his radicalised youngest son Mettus - but since Hudak refuses to be treated, Phlox must wait. Eventually, Hudak reflects on Phlox's words and agrees to the lifesaving procedure. A détente is then reached in which the three Denobulans are granted passage home aboard Hudak's vessel.