When the planet Empyrea, a colony of genetically perfected human beings, demands that the Federation remove a science station which has been in place for nearly twenty years, the "Starship Enterprise™ " is assigned to transport to the planet the Federation ambassador who negotiated with the Empyreans long ago -- an ambassador who was once Dr. McCoy's closest friend, but is now a bitter rival.

On Empyrea, McCoy discovers Anna, a daughter he never knew he had. McCoy soon realizes that the isolationist Empyreans must not learn her father is an off-worlder, and that her genes are less than "perfect." As relations with the Empyreans collapse around him, McCoy must find a way to save his newfound daughter from the harshest penalty her planet can impose!