Historian and sociologist John Gill has stopped responding to transmissions. He is embedded in the Ekosian population to study it. Investigating, Kirk and Spock discover that Ekos has developed nuclear weapons - an achievement well ahead of where they should be scientifically, based on past probes. And they have modeled their society on Nazi Germany, right down to oppression of their sister planet, Zeon. It seems apparent Gill has contaminated this society, but why? And why Nazi Germany?