"Errand of Mercy" is an episode of the original science fiction television series Star Trek. It was first broadcast on 23 March 1967. It is episode #26, production #27, written by Gene L. Coon and directed by John Newland. This episode was the first in which the Klingons appeared.

With a war with the Klingons declared, Captain Kirk and his First Officer, Mr. Spock, attempt to sway the incomprehensibly placid population of a planet to resist an invading military occupation.

Relations between the United Federation of Planets and the Klingon Empire have reached the breaking point, and recent negotiations have collapsed. The starship Enterprise has been sent to the world of Organia, a non-aligned planet near the Klingon border, to prevent the Klingons from annexing it. As the Enterprise approaches Organia, Spock briefs Kirk, calling it a primitive society. Without warning, the Enterprise is attacked by a Klingon vessel, which is quickly destroyed when the Enterprise returns fire.

Upon arrival at the planet, Kirk leaves his helmsman, Lieutenant Sulu, in command of the ship with instructions to withdraw if a Klingon fleet arrives. Kirk and Spock then beam down to the planet surface and find themselves in a primitive town, with ruins in the distance. Kirk tells the Organian council what the Klingons will do if they capture the planet, but the Organians are unconcerned. Instead, the Organian leader says that the Enterprise and her crew are the only ones in danger. A Klingon fleet appears, firing on the Enterprise. Kirk orders Sulu to withdraw, which strands Kirk and Spock on the planet.

The Organians disguise Kirk as one of them and have Spock pose as a Vulcan merchant of trillium. The Klingons seize control of the planet without resistance and install the ranking Klingon officer, Kor, as the military governor. Kor, noticing that Kirk is the only Organian who doesn't smile all the time, takes a liking to him and demands that he act as the Organian liaison. Spock is taken for questioning to verify his background as a trader but resists the "mind sifter" device that the Klingons use.

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