The Conscience of the King

Dr. Leighton calls Enterprise to his home on Planet Q with the promise of a new food source that could end hunger. But this is a ruse: Leighton is one of the few remaining survivors of Kodos the Executioner, who used a planetary famine to apply his own ideas of eugenics on Tarsus IV years earlier. A burned body convinced authorities that Kodos had died then, but Leighton is certain that actor Anton Karidian is Kodos.

Synopsis adapted from TVmaze (CC BY-SA 4.0)