"The Devil in the Dark" is William Shatner's favorite episode. It is also one of my favorite episodes. The program is pure Star Trek because it deals with one of the series' main themes: the respect for other life forms. I do not think one could get a clearer example of one of the show's most interesting ideas. In this episode, Kirk and his crew have to confront a monster that is killing miners on a distant planet. The story is an excuse to explore the right that humans have to destroy creatures that are a vital part of the environment. Today's concerns with environmental causes make the show more relevant now than ever before. It is extremely well written and performed with gusto by our beloved cast. One memorable sequence involves Spock joining with the mind of the monster. Plenty of tension between Spock and Kirk (they want to solve the problem using different methods) adds to the fun. Shatner and Leonard Nimoy do some of their best work here.