Enterprise visits a Federation colony and gets into a conflict with the crew of a Klingon ship.
This is an enjoyable episode with strong anti-war themes and some quite memorable moments.
The story contains many elements covered in previous episodes such as 'The Errand of Mercy', 'Wolf in the Fold', and the numerous occasions the crew have found themselves either under the control of more powerful and malevolent beings. It's not perfect, but the plot unfolds in an entertaining way.
I particularly liked this portrayal of the Klingons. It feels closer to the warrior portrayal that payed off so well in 'The Next Generation' and 'Deep Space Nine'. The characters Kang and Mara are integral to the plot and involved in some of the most memorable scenes. Michael Ansara gives probably the best performance of the episode.
The central theme about powerful influences upon hatred and war that feed off conflict between people is an important subject. It was particularly relevant when this episode was made and works as an effective commentary of the Cold War. Sadly it is still pertinent today, as the world is more divided then ever with institutions like governments, media, and the defence industry continuing to profit from conflict as much as ever.
We see crew members displaying irrational signs of hatred, bigotry, and a desire for revenge that is quite ugly. One scene involving Chekov is particularly dark for Star Trek.
Not all of it holds up to a modern viewing. There are some quite silly moments involving swords and some of the acting from William Shatner and Deforest Kelley strays over the top. It also trowels on its key messages with some quite preachy exchanges of dialogue.
Visually it is hit and miss for me. I like the alien special effects, set design, props, and costumes. The Klingon boot polish type makeup is not particularly good, nor the choreography of the sword fighting.
Leonard Nimoy and George Takei have solid outings as their characters appear to be the only two regulars who do not lose rationality amongst all the chaos.
For me it's a 7.5/10 but I round upwards.