At the request of the Denobulans, Enterprise goes to rescue a group of geologists from a planet now being run by xenophobic militants. All off-worlders must go. Being an experienced spelunker, Ensign Mayweather leads Commander Tucker and Lt. Reed on the rescue mission underground. They have three days before the government comes after them.
While in orbit, Enterprise comes to the aid of a transport suffering from a dangerous radiation leak. The most seriously injured of the various aliens is Hudak– an Antaran, whose species has long been in conflict with the Denobulans. Though suffering from a fatal case of radiation poisoning (if left untreated), he refuses help from Dr. Phlox– who reluctantly complies, since Denobulan medical ethics places the patient's wishes above all other considerations. Phlox, for his part, is upset at the mutual hatred between the two species (it is a long standing source of tension between him and his son Metis) but since Hudak refuses to be treated, Phlox cannot do so.
Underground, Mayweather gets injured while saving Reed and Tucker from sliding down an abyss. Leaving Mayweather behind, Reed and Tucker find the Denobulan geologists. Time is running out, but the scientists don't want to leave. Tucker uses cunning diplomacy (i.e. he threatens to use his phase pistol) to get the geologists to safety.
With diplomacy of his own, Phlox follows Captain Archer's orders to try to help Hudak. Eventually, Hudak agrees to Phlox’s lifesaving procedure. Though the transport will now have three Denobulans aboard, a détente is reached– both sides are willing to share the ship.