Minimal Spoiler:

> Nearing Eminiar VII, the Enterprise receives a message from the planet warning them not to approach, but Ambassador Fox orders Captain Kirk to proceed. Kirk, First Officer Spock, and additional security personnel beam down to the planet, where they are met by representatives Mea 3 and Anan 7. During a supposed attack by Vendikar, Anan 7 explains that the war is conducted as a computer simulation, and that the Enterprise has been "destroyed" in the attack. The two planets have a treaty, according to which they must kill the "victims" of every simulated attack. The crew are therefore expected to report to Eminiar's disintegration chambers for execution, and Kirk's party is taken captive.

[0] https://en.wikipedia.org/wiki/A_Taste_of_Armageddon