Starring William Shatner, Leonard Nimoy
Guest Stars: DeForest Kelley, Grace Lee Whitney, George Takei, James Doohan, Edward Madden
Directed by Leo Penn
(actor & director credits courtesy IMDB.com)
An accident with the transporter splits Kirk's good and evil halves into two separate people, and maroons Sulu and other crewmen on a dangerously frigid world.
Writer Richard Matheson, well known for his quality work on The Twilight Zone and books like The Incredible Shrinking Man and I Am Legend, crafts a worthwhile futuristic Jekyll and Hyde tale in as far as I know his only script for a Trek series. Shatner's performance as the evil Kirk is at times over the top, but entertainingly so, and the scenes with both Kirks are well-filmed and convincing. This episode also features the first Vulcan nerve-pinch as well as our first indication of romantic feelings between the Captain and Janice Rand, a storyline which would eventually peter out. It's one of the best of the series' early episodes, with some fine interplay between Kirk, Spock, and McCoy.