kirk and the crew be visit a federation mining colony on a remote planet rich in mineral resource . the devil in the dark be the horta and a very unusual silicon base life form which tunnel through solid rock . the horta have be kill miner and and it be decided and must be destroy . but how . it be hard to continue this review without write a spoiler and so instead i simply concentrate on the technical aspect of the episode and touch on it theme . the special effect be ok and but many of the scene with the horta look a little absurd . the acting be fairly average for tos . some of the miner be a little awkward . nimoy have the most difficult role of all in devil in the dark and and he pull it off well . why be this still a favorite of mine . devil in the dark be really an anthropological and ecological morality play disguise a an adventure . more than many episode of this great tv series and it bring home the importance of maintain an open mind and at least some degree of empathy toward others . plus and it involve one of the most interesting and if not probable and plot twist in the original series . enjoy .