Enterprise is asked to evacuate a group of Denobulan geologists from Xantoras, a world that has been taken over by a militant faction. The Denobulans are located in some underground caverns, so the rescue team — Mayweather, Trip and Reed — will have to traverse some treacherous rock formations in order to get them out. Meanwhile, another ship of off-worlders is headed away from Xantoras when their reactor casing is ruptured, flooding the ship with radiation. When the Xantoran officials refuse to let the ship land, Archer agrees to bring the evacuees onboard Enterprise for treatment. One of the evacuees is an Antaran named Hudak, who is horrified that Enterprise's doctor is Denobulan. Phlox explains to Archer that the Denobulans and Antarans have a troubled, bloody history between them — the two species have gone to war several times. Even though it's been three hundred years since the last conflict, much bad blood still exists between them.