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The Enemy Within 

A transporter malfunction splits Captain Kirk into two halves: one meek and indecisive, the other violent and ill tempered. The remaining crew members stranded on the planet cannot be beamed up to the ship until a problem is fixed.


Leo Penn


Richard Matheson, Gene Roddenberry (created by)




Episode complete credited cast:
William Shatner ... Capt. Kirk
Leonard Nimoy ... Mr. Spock
DeForest Kelley ... Dr. McCoy
Grace Lee Whitney ... Yeoman Janice Rand
George Takei ... Sulu
James Doohan ... Scott
Ed Madden Ed Madden ... Fisher (as Edward Madden)
Garland Thompson Garland Thompson ... Wilson
Jim Goodwin Jim Goodwin ... Farrell


While beaming back aboard the Enterprise, a transporter malfunction results in two vastly different Captain Kirks being beamed aboard. His personality has in effect been split into two. One Captain Kirk is weak and indecisive, fearful of making any kind of decision; the other is a mean-spirited and violent man who likes to swill brandy and force himself on female crew members. Meanwhile, as Scotty struggles to repair the transporter, the landing party is stuck on the planet below with temperatures falling rapidly. Written by garykmcd

Plot Summary | Plot Synopsis


TV-PG | See all certifications »






Release Date:

6 October 1966 (USA) See more »

Company Credits

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Technical Specs


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Did You Know?


This was the first episode, in production order, to feature the Vulcan Nerve Pinch. The episode which aired the previous week, Star Trek: The Original Series: The Naked Time (1966), was filmed afterward. See more »


Evil Kirk's phaser changes between cuts in the shoot-out in Engineering. See more »


Captain James T. Kirk: Yes, Mr. Spock, what is it?
Mr. Spock: Is there something that I can do for you, Captain?
Captain James T. Kirk: Like what?
Mr. Spock: Well, Dr. McCoy seemed to think I should check on you.
Captain James T. Kirk: That's nice.
See more »

Alternate Versions

Special Enhanced version Digitally Remastered with new exterior shots and remade opening theme song See more »


Referenced in Saturday Night Live: William Shatner/Lone Justice (1986) See more »


Theme From Star Trek
Written by Alexander Courage
See more »

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User Reviews

The Shadow Kirk
20 December 2016 | by Rainey-DawnSee all my reviews

Season 1, episode 5. The Enterprise is on a mission on the planet Alpha 177. Geological Technician Fisher is beamed aboard first with a strange yellow substance on his uniform. Next Captain Kirk is beamed up and feeling a bit strange so Scotty helps to escort him down the hall... as soon as they leave another Kirk appears on the transporter floor. Some how the transporter has split Kirk into to halves: One gentle & benign while the is other a madman & a malice. This alternate Kirk is very mean, even causing Yeoman Rand some problems so she ended up scratching him and that is the true identifying mark of the "evil Kirk". There are more problems because there are more members of the Enterprise down on the planet surface ready to beam aboard but they cannot beam up because of the transporter problems, fearing they will be split as well, and the temperatures on the planet are dropping to well below freezing into the negative numbers.

A very good and even thought provoking episode. The idea of the "Shadow Self" splitting from oneself - Jungian psychology teaches us of our inner Shadow.


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