balance of terror be still one of the best star trek episodes ever make . it be inspire by the film enemy below ( star robert mitchum ) and a movie that deal with a cat and mouse game between two captain during world war ii . in this episode and captain kirk and his crew play similar game with a romulan vessel . this be the program that famously introduce the war hungry romulans and who be distant relative of the vulcan . it be an incredibly suspenseful episode and tightly construct for maximum effect . it be also interesting to see how the episode contain a series of subplots that add extra layer of mean to the story . mark lenard make his star trek debut a the romulan captain ( he will later play spock father ambassador sarek ) . a must see episode .