Enterprise visits the planet Dekendi III hosting an Interspecies Medical Exchange conference. Dr. Phlox requests the Vulcan delegation provide him with the latest research on a terminal neurological disease called Pa'nar Syndrome without revealing that T'Pol is infected. Pa'nar Syndrome is a rare illness associated with mind melders, a sect ostracized by Vulcan society. A forced mind meld against her will infected T'Pol in the episode Fusion. She tries to keep her disease a secret while Dr. Phlox researches treatment methods. Meanwhile, one of Phlox's wives, Feezal, visits Enterprise to install a neutron microscope and begins flirting heavily with Trip. He is uneasy that a colleague's wife is making overt sexual advances toward him.

The Enterprise finds a small, disabled ship drifting in space and discovers it contains a human corpse. More questions arise when the Suliban and Tholians each claim the craft. Both alien species attack the Enterprise and later each other to seize the derelict.