the devil in the dark be william shatner favorite episode . it be also one of my favorite episode . the program be pure star trek because it deal with one of the series main theme represent the respect for other life form . i do not think one could get a clear example of one of the show most interesting idea . in this episode and kirk and his crew have to confront a monster that be kill miner on a distant planet . the story be an excuse to explore the right that human have to destroy creature that be a vital part of the environment . today concern with environmental cause make the show more relevant now than ever before . it be extremely well write and perform with gusto by our beloved cast . one memorable sequence involve spock join with the mind of the monster . plenty of tension between spock and kirk ( they want to solve the problem use different method ) add to the fun . shatner and leonard nimoy do some of their best work here .