"The Devil in the Dark" is a first season episode of the original science fiction television series, Star Trek, first airing on March 9, 1967, and repeating on June 15, 1967. It was written by Gene L. Coon and directed by Joseph Pevney. William Shatner wrote in his memoirs that "The Devil in the Dark" was his favorite original Star Trek episode. He thought it was "exciting, thought-provoking and intelligent, it contained all of the ingredients that made up our very best Star Treks". In the documentary 50 Years of Star Trek, Leonard Nimoy also named "The Devil in the Dark" as an "interesting episode", stating "I thought [it] was a wonderful episode about the fear of the unknown, how we fear and even hate something that we don't know anything about, learn who your enemy is, and it's not, maybe then it's not no longer your enemy."

In this episode, Captain Kirk and Spock face off with a deadly subterranean creature.

Enterprise arrives at the pergium mining colony on planet Janus VI to help the colony deal with a creature that has killed 50 miners and destroyed equipment with a strong corrosive substance. Kirk, Spock, and McCoy meet with the mine supervisor, Chief Engineer Vanderberg and an engineer, Appel, who describe the amorphous creature and its behavior. During the briefing, Spock's attention is drawn to a spherical object on Vanderberg's desk, which Vanderberg dismisses as a worthless silicon nodule, saying that there are thousands of them in the mines, and that they are a mere geological oddity. Suddenly, they are alerted to a problem in the colony's main nuclear reactor, and find its guard killed and the main circulation pump stolen. Chief Engineer Scott rigs a temporary replacement that will prevent critical failure, but a more permanent solution must be found in 48 hours.

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