In 2266, he lived with his parents at the Deneva colony. Late that year, travelers from Ingraham B brought neural parasites to the colony; over the next eight months, these parasites infiltrated and overwhelmed the colony, infecting nearly everyone. By the time of the Enterprise's 2267 visit, Peter and Aurelan were infected and George had died, presumably resisting the parasites' control. Though Captain Kirk discovered how to destroy the parasites in time to save Peter and the colony, his discovery came too late to save Aurelan.
Peter Kirk was portrayed by Craig Hundley.
A filmed scene cut from this episode featured dialog between Kirk and his nephew Peter. The dialog concerned Peter's returning to Deneva to live with Sam Kirk's partner.  The scene was edited from the episode.