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.

Enterprise visits an idyllic planet, where McCoy encounters a large white rabbit that is "very late". And shortly afterwards, a little girl who is following him. McCoy isn't becoming insane; it soon becomes apparent that thinking about a thing will cause it to materialize, as everyone encounters people and things from their past or their fantasies. But something on the planet's surface is draining power from Enterprise. And then McCoy, convinced that what he sees is a harmless illusion, confronts a charging knight - and dies, pierced through the heart! What kind of odd world is this, and how can the ship and crew escape it?