While exploring a "hypergiant", Enterprise makes first contact with an alien race known as the Vissians, and the two starships' crews begin to intermingle. Commander Tucker, becomes intrigued when he meets a Vissian couple in the mess hall accompanied by a third member of their race, and learns that the being, which has no name, is a "cogenitor" - a third gender in Vissian biology. Cogenitors are needed to complete reproduction: they do not genetically contribute to offspring, but supply an enzyme required for fertilization. Since cogenitors only constitute 3% of the population, Vissians must apply to have a cogenitor assigned to them when they intend to conceive a child.
Meanwhile, elsewhere on the ship, Lieutenant Reed finds himself the romantic focus of a Vissian crewmember - their tactical officer. Similarly, Captain Archer bonds with the alien captain whilst on a 3-day reconnaissance of the star in a small probe. Tucker, however, becomes increasingly intent on the rights of the cogenitor and learns, with the help of Doctor Phlox, that they are actually equally intelligent. On the alien vessel, without the couple's knowledge, Tucker secretly encourages the cogenitor to learn to read, while building a friendship with it. Despite having a near-total lack of education available, it is an insatiable learner. Soon learning the importance of names, it then asks be called Charles (Commander Tucker's own first name).
'Charles' soon realizes that "her" life in Vissian society would be unfulfilling; she then leaves and requests political asylum. Archer now returns to find himself in the middle of a first contact diplomatic crisis, with the Vissians confused and defensive at Tucker's interference in their traditions. Tucker appeals to Archer's sense of justice, but he sides with the Vissians. With the cogenitor returned, the Vissians hope good relations with the humans can continue. Later communications however reveal that the now despondent Charles has committed suicide, thereby delaying the birth of the Vissian's child. Archer then summons Tucker and severely reprimands him for his lack of professionalism and judgment.