Enterprise is asked to evacuate a group of Denobulan geologists from a world that has been taken over by a militant faction, and since they are located deep underground, the effort requires some treacherous spelunking by the rescue team. Meanwhile Phlox faces a dilemma when another evacuee, an Antaran afflicted with a fatal dose of radiation, refuses to be treated by a Denobulan because of very old bad blood between the two races.
