It has been eighteen months since the end of the original five-year mission. Captain James T. Kirk, now an admiral, is on Earth, in a new relationship, overseeing the refit of his beloved ship. Plans are to hand it over to its new captain, Willard Decker. Kirk meets a scientist, G'Dath, who has invented a device that could tip the balance of power for the Federation and the Klingons. Both sides pursue the man. Kirk and his former crewmate, Kevin Riley, attempt to save the day.