Spock's Brain

Stardate 5431.4: The Enterprise is intercepted by a starship of unknown design and a woman from the ship beams directly into the bridge and uses a device to render the Enterprise's crew unconscious. She then walks over to Spock... When the crew awakens, McCoy summons Kirk to sick bay and informs him that the alien visitor apparently removed Spock's entire brain without even performing surgery. After Spock's body is fitted with a device that allows McCoy to control the Vulcan's motor functions with a remote control, Kirk starts a search for Spock's brain, hoping it can be recovered and somehow returned to Spock before his body decays.