"Spock's Brain" is the first episode of the third season of the original science fiction television series, Star Trek, first broadcast September 20, 1968. It was the first episode to air after NBC moved the show from 8:30 P.M. to 10 P.M. on Friday nights. It was repeated July 8, 1969. It is episode #56, production #61, written by Gene L. Coon (under the pseudonym Lee Cronin) and directed by Marc Daniels.

In this episode, an alien female beams aboard the ship and, after incapacitating the rest of the crew, surgically removes Spock's brain. Kirk and the crew have just hours to locate and restore it before Spock's body dies.

On stardate 5431.4, the Federation starship USS Enterprise, under the command of Captain James T. Kirk, encounters a curious ship of unusual design. Upon contact, the ship emits a transport beam and a mysterious woman appears on the Enterprise bridge. She stuns the entire crew using a bracelet-like device, then examines each of them, taking particular interest in the Vulcan First Officer Spock. When the crew awakens, Chief Medical Officer Dr. McCoy finds Spock lying on a bed in Sickbay with his brain surgically removed. Thankfully, owing to his unusual Vulcan physiology, Spock's body can survive in this "brainless" state mechanically, giving Captain Kirk about 24 hours to find his stolen brain.

Sensors detect the ship's ion trail and Kirk follows it to the Sigma Draconis system. The system contains three planets that are reported to be inhabited: Sigma Draconis III, IV and VI. However, the recorded technological levels of each world are determined to be incapable of producing the kind of spacecraft that the Enterprise followed there. The sixth planet however, which shows no sign of industrial advancement at all, radiates energy transmissions that Communications Officer Lt. Uhura describes as contradictory to its technological scale. Playing on the hunch that the planet may be deceiving, Kirk beams a landing party to the surface.

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