Stardate 2817.6: Kirk is attending a performance of MacBeth with Dr. Leighton, on Planet Q. Leighton is obsessed with Anton Karidian, the man playing MacBeth, and insists he is Kodos the Executioner. Back on board the ship, Kirk notes that Leighton diverted them to Planet Q claiming he had devised a new synthetic food source. Leighton admits he lied to get Kirk there. Kirk claims Kodos died but Leighton doesn't believe it and notes that 4,000 people were killed. Leighton's wife Martha can't get through to her husband either. The disfigured Leighton warns that there are only a few survivors of the massacre and notes he invited the acting company to a party that night.
Back on board, Kirk researches Kodos, Governor of Tarsus 4 who evoked martial law and slaughtered half of the colony and whose body was never confirmed. Karidian's history is vague and the photos of the two men are similar. Kirk decides to attend the party where he finds Leighton has temporarily gone into town. The captain notices Karidian's daughter Lenore present, and she notes her father rarely meets with his public. Kirk and Lenore flirt and they go out for a walk. They start to kiss but Kirk spots Leighton's body in the rocks.
Believing that Leighton's suspicions were confirmed, Kirk contacts the captain of the company's ship and asks him to strand them so he can take them on board. Later Lenore arrives to ask for passage and she offers a special performance as payment. He agrees and orders the ship off course to deliver them.
En route, Kirk reviews the list of survivors of the Tarsus massacre. Upon learning that Lt. Riley is one of the survivors and aboard the ship, Kirk demotes him to engineering. Puzzled, Spock goes to Dr. McCoy who doesn't see a problem. Kirk shows Lenore the observation deck and they end up kissing. Meanwhile, Spock checks the computer records about Kodos and Tarsus 4 and tells his findings to McCoy about how Kirk and Riley are the only two remaining eyewitnesses of the Kodos Massacre, after the governor was forced to sacrifice 4,000 people to provide the other 4,000 with enough food to survive. The other eyewitnesses are dead… and the Karidian Players have always been nearby.
Riley is working in Engineering and calls up to the rec room for company. As Uhura sings for him, Riley's unaware that an unseen hand has put poison in his milk. He drinks it and collapses. Fortunately, they hear him over the intercom and he recovers in Sickbay. Spock warns that if Riley dies, Kirk will be the next target.
Spock and McCoy go to Kirk and the doctor reveals Riley will probably survive, and confront him about what Kirk is trying to do. Kirk claims to be interested in justice rather than vengeance, but admits he isn't sure. Later Spock meets with Kirk again when they hear the sound of a phaser overload. Searching Kirk's cabin, they find the phaser and tosses it out through a disposal hatch.
Kirk goes to see Karidian and asks him flat out if he is Kodos. Karidian hedges his answer and Kirk has him recite one of Kodos speech to make a voiceprint they can use to verify his identity. Karidian recites the speech as if by memory and notes that Kodos might have been a hero if the supply ships had not arrived in time. Karidian admits he's fallen into depression and despair and Kirk leaves him… only for Lenore to confront him over his treatment of her father. She's furious over his use of her to get at Karidian. Meanwhile, Riley has recovered and overhears McCoy talking about Kodos.
The Karidian Players begin their performance of Hamlet while Kirk and Spock determine Karidian's voice is a close match for Kodos'. McCoy reports that Riley has taken a phaser and disappeared. Kirk goes to the theater where he finds the armed Riley backstage. The captain tries to convince Riley to give up the phaser while Karidian overhears them from the stage. Riley gives up the phaser and goes back to Sickbay while a shocked Karidian laments the voice from the past he has heard. Lenore tries to assure him and announces she will kill the last two eyewitnesses. Unaware until now of what Lenore has done, Kodos says he now has nothing. Kirk overhears them and the clearly crazed Lenore sees him. She draws a phaser and runs out on stage. She tries to shoot Kirk and Karidian leaps in the way. She mourns over his body as the audience looks on.
Later as they prepare to leave orbit, McCoy reports that a crazed Lenore is receiving treatment and still believes her father is alive, performing to the crowds. McCoy wonders if Kirk will answer his question that he cared for Lenore… then realizes he has his answer.