Episode Title: "OPERATION -- ANNIHILATE!"
Production Number: 29
Original Air Date: 04-13-67
Stardates: 3287.2, 3289.8
The U.S.S. Enterprise approaches the colony planet Deneva -- home of Captain James Kirk's brother, Sam, and his family -- but the Enterprise cannot make contact with Deneva. A Denevan ship is detected heading towards the sun, and the crazed pilot declares he is finally free just before his ship burns up.
Commander Spock determines a pattern of mass insanity destroying civilizations in a straight line across the Galaxy, starting with the ancient civilizations in the Beta Portilin system; 200 years ago, Lavinius Five was swept by mass insanity, than Pheta Signi Twelve, and the last was Ingriam B two years ago. Deneva is the next planet in line.
Captain Kirk leads a landing party to Deneva, and finds the population in a violent and agitated state. Kirk finds his brother, Sam, dead and his nephew, Peter, is infected with an unknown condition. Sam's wife, Aurelan, is terrified and hysterical, and tells Captain Kirk that eight months ago visitors from Ingriam B brought alien creatures aboard their ship, against their will, to Deneva. The aliens are infecting and controlling the population. Just before she dies, Aurelan warns that the aliens are forcing the infected humans to build ships to spread to another planet.
While on Deneva, Spock is infected by one of the alien life forms -- flying, single-celled organisms resembling individual brain cells in a larger creature -- and he tries to take control of the Enterprise before being restrained. Spock uses his mental discipline to fight the pain the infection is causing, and he beams down to the planet to retrieve one of the alien cells.
Spock and Dr. McCoy experiment on the creature, but can find no way to destroy the aliens without killing all humans on the planet. Kirk suggests that bright light might harm the aliens, which is why the Denevan who flew into the sun was freed of the infection. Spock volunteers himself to be exposed to an intense light, and it succeeds in destroying the alien infection, but also blinds the half-Vulcan first officer.
Dr. McCoy determines that only ultraviolet light is needed to destroy the aliens and free the Denevans they have infected. The Enterprise deploys 210 ultraviolet satellites around the planet to bombard Deneva with light and destroy the creatures, before heading for Starbase 10. Spock regains his sight, because Vulcans have an inner eyelid to shield against the bright Vulcan sun.
Factoid: There are almost a million inhabitants of Deneva.
Factoid: There are 14 science labs aboard the U.S.S. Enterprise.
Guest Characters: Nurse Christine Chapel, Lt. Leslie, *George Samuel Kirk dies, *Aurelan Kirk dies, *Peter Kirk
KEY: [brackets]=illusions *star=first appearance