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. Kirk is less than amused at the deception - and then someone murders Leighton. It's not enough to accuse, but it is enough for suspicion, so Kirk arranges to strand the acting troupe, and then offers them a ride on Enterprise where he hopes to ascertain whether Leighton's accusation is true.