The USS Enterprise ventured to Eminiar VII in NGC 321, with Ambassador Robert Fox on board to foster diplomatic relations. Unfortunately, only a little is known about Eminiar VII other than they have been actively engaged in a conflict with the neighboring world, Vendikar.

As they came closer to Eminiar VII, a communication was received from the planet, cautioning the Enterprise not to approach. However, Ambassador Fox commanded Captain Kirk to move forward. Kirk, Spock, the first officer, and other security personnel beamed down to the planet, where they were welcomed by Mea 3 and Anan 7. During a simulated attack from Vendikar, Anan 7 informed them that the war was run through a computer and that the Enterprise had been "obliterated" in the attack. The two planets had a treaty that necessitated killing the "victims" from each simulated attack. Hence, the crew was expected to report to Eminiar's disintegration chambers to be executed. Kirk's team was taken captive, but Spock used telepathy to place a suggestion in the jailer's mind, allowing them to escape.

Anan 7 employed a voice duplicator to sound like Kirk and command the team to transport down. Scotty, feeling dubious, had the ship's computer inspect the transmission and confirm that it was bogus. Next, he commanded the shields to be raised. When the crew failed to transport, Eminiar opened fire on them, but the shield deflected the defense. Anan 7 then communicated with the Enterprise, asserting that the attack was due to a technical hitch. Ambassador Fox, deciding to trust Anan, beamed down and was taken to a disintegration chamber with Mea 3, who had also been "slain" in the war game. Spock and the security officers saved them.

When Kirk meets Anan 7, their guards soon overpower him and are confined in the council chamber. He immediately commands Scotty to initiate General Order 24 and warns them of the planet's impending destruction in two hours. This causes chaos in the room, and Kirk uses the opportunity to snatch away the weapons from the guards. With Spock's assistance, Kirk then demolishes the war simulation computers. Anan 7 rebukes Kirk for his choices, arguing that fighting wars without the simulation is impossible. Kirk, however, believes that the simulation has kept the war going for too long by sheltering both societies from its consequences. He persuades Anan 7 to halt the war and begin peace negotiations, and Fox steps in as an impartial mediator between the planets.