The mutual distrust between the Klingons and the Federation becomes the center of attention for Kirk when he takes Klingon prisoners aboard the Enterprise for trespassing in Federation space and attacking a Federation outpost. Once aboard the ship, an alien entity that thrives on hostility allows the opposing forces to lock into a repetitive cycle of combat—allowing an equal number of Kirk's men for every Klingon on board to fight above decks in a sort of arena of violence.
"Day of the Dove" isn't great, but it's good—showing more promise than many third-season offerings. Michael Ansara as Kang provides a good adversary for Kirk, as the distrust between the two sides elevates into an all-out battle of swordplay, courtesy of the animosity-inducing alien presence.
The "violence is bad" message is pretty obvious, but it manages to work fairly well in the story's context. I particularly liked the scene where Kirk and his crew come to realize that they're feeding off racially motivated hatred, even if it was a little overplayed. The end provides a classic Trek solution, where the two sides end hostilities to be rid of the alien entity's cycle of pointless bloodshed. Not groundbreaking, but respectable.
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Next episode: For the World Is Hollow and I Have Touched the Sky