Star Trek (1966–1969)
25 user 6 critic

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)

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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 »

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Did You Know?


The unit that the evil Kirk accidentally phasers in engineering was recycled as the housing for the main circulating pump for the PXK pergium reactor in Star Trek: The Devil in the Dark (1967). See more »


There are 5 Captain's Log entries. Kirk makes the first 4 entries on the following Star Dates: 1672.1, 1672.9, a supplemental entry at 1673.1, and 1673.5. The last Log entry is then made by Spock at 1673.1 again, showing that his log entry should have occurred at approximately the same time as the supplemental entry, rather than after Kirk's last entry. See more »


Captain James T. Kirk: Help me. Somebody... make the decision.
Mr. Spock: Are you relinquishing your command, Captain?
Captain James T. Kirk: No. No, I'm not.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: Well, then, we can't help you, Jim. The decision is yours.
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Alternate Versions

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


Featured in Cinematic Excrement: Spock's Brain (2014) See more »


Theme From Star Trek
Written by Alexander Courage
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User Reviews

The Most Brutal, Thoughtless Captain Kirk
22 June 2006 | by BogmeisterSee all my reviews

The title itself is misleading in this episode and so are the first few scenes. The second Kirk who materializes on the transporter platform after a strange malfunction is not a duplicate of the real Capt. Kirk, nor is he, as it turns out, an enemy to Kirk's existence. Kirk himself gets it wrong as he describes what happened in his log. Neither of the Kirks after the credits is the real one in this episode. They are both half of the real Kirk, who no longer exists at this point. The meek, mild half is more difficult to notice as not being quite real while his confidence slips away more gradually. The violent, animalistic half gives himself away more easily as he demands Saurian brandy from Dr. McCoy and then tries to rape Yeoman Rand. Yes, the crew who encounter him still believe it's Capt. Kirk, but it's as if he's taken some bad drugs lately - not very captainly behavior.

Shatner gets to tap into his inner rage with his performance as the so-called evil Kirk version in this episode. This version of Kirk is always sweating, eyes furtive, and then usually spasming into a screaming fit as if totally out of control or seriously ill. It's a startling transition whenever we switch from the calm, tired Kirk (also ill, tho in a benign fashion) to this obvious madman (the lighting in these scenes also helps). However, by the 3rd act, we learn, via Spocks's analytical observations, that all of Kirk's power of command rests in this evil half. Of course, the entire episode debunks the whole simplistic concept of good and evil; the supposed negative side of Kirk is needed for him to function as captain. We humans are made up of many parts, this story says, and all of these are necessary, whether labeled positive or negative (one can say the same for business and political leaders).

This episode has some pretty intense moments, especially the scene of the negative Kirk attacking Rand - it's a bit too real and is uncomfortable to watch, a disturbing depiction of attempted rape. I'm not sure what to make of Spock's snide remark to her at the end - maybe his intent was to diffuse the whole thing, but it seemed quite inappropriate - though she just took it in stride. The glaring flaw in the episode, in retrospect, is that no shuttlecrafts were sent to rescue the men trapped on the planet below from freezing to death. Maybe the crafts were all in disrepair or there was something in the atmosphere (or maybe they weren't written into the show, yet). Of course, this added dilemma of crew members slowly dying served to underscore the positive Kirk's growing indecision on such matters. It was probably in this episode that we first learned how infallible a starship captain must be, even if just for the sake of appearance.

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