(written from a Production point of view)
A transporter malfunction splits Captain Kirk into two people – one good and one evil, and neither capable of functioning well separately.
During a survey of Alfa 177, geological technician Fisher slips down a rock, gashing himself badly and smearing his uniform with a strange magnetic type of ore. He beams up to the USS Enterprise for treatment. Detecting a curious overload in the transporter circuitry, Lieutenant Commander Montgomery Scott has Fisher decontaminated before reporting to sickbay, but the problems have already begun; the strange ore has altered the function of the transporter. Next, Captain Kirk beams up from the planet, before the fault is discovered. He apparently materializes normally – but is, in fact, a shadow of himself.
Due to this transporter accident, Kirk is split into two beings. The first to materialize embodies all of Kirk's positive qualities. Moments later, after everyone has left, Kirk's evil twin materializes. Some time passes before the mishap is discovered. He demands Saurian brandy from McCoy in sickbay and proceeds to roam the ship drunk. McCoy goes to Spock about this who goes to the good Kirk about what the good doctor tells him. Kirk shrugs it off telling Commander Spock that McCoy was just pulling his leg. The evil duplicate Kirk, who was now instinctively drawn to Janice Rand, was alone with her in her quarters, drunk and amorous. The duplicate Kirk mentioned to her the feelings they'd been hiding, claiming she was "too beautiful to ignore," and "too much woman," and that they have both been "pretending too long." The duplicate Kirk suddenly grabbed Rand and starting kissing her very hard and rough. As she was fighting back, the duplicate Kirk pushed her to the floor and attempted to rape her, but she defended herself and left a large scratch on the duplicate Kirk's face. During the struggle, the evil Kirk attacks crewman Fisher. In sickbay, Rand tells the good Kirk, plus Spock, and McCoy that the captain tried to assault her in which both her and Fisher accuse him of this. Kirk firmly denies this whereupon Spock deduces that there is an impostor of him aboard the Enterprise.
Scotty finds that the yellow ore Fisher beamed up with somehow caused an overload in the transporter. The transporter does indeed work but they dare not use it for risk of duplicating Sulu and the rest of the landing party. Kirk tells Spock that he must inform the crew of what has happened to him, since they deserve to know. Spock, with all due respect, tells Kirk that as he is the captain, he cannot afford to be anything less than perfect in the eyes of the crew. If he does, the crew loses faith in him – and he loses command. Kirk knows this and wonders why he just forgot it just now. Later, on the bridge, Kirk makes an announcement to his crew from his chair about the impostor aboard. While making the announcement, his evil half is rummaging through the captain's quarters. Good Kirk informs the crew that the impostor can be identified by scratches on his face. Evil Kirk angrily destroys the captain's desktop monitor and rants at the top of his lungs "I'm Captain Kirk... I'M CAPTAIN KIRK!!!"
Evil Kirk goes to good Kirk's mirror and finds make-up on the table. He applies some of it to his scratches and they are now barely visible. He opens the door to good Kirk's quarters and finds Crewman Wilson walking down the corridor near the room. He asks Wilson for his phaser. Wilson hands it over and is promptly knocked out. Later, both the good Kirk and Spock in the briefing room try to figure out where Kirk would go on the Enterprise to elude a search. Good Kirk quickly deduces that the evil Kirk is hiding in the lower levels of the ship – the engineering deck. He and Spock head there. In main engineering, a cat and mouse game ensues between the two Kirks and they confront each other. Just as the evil Kirk is about to kill the good Kirk, Spock knocks him out with the Vulcan nerve pinch, but not before the phaser discharges and disables the transporter ionizer with a phaser shot, making it harder to rescue Sulu and the landing party who are trapped on the rapidly freezing planet.
Meanwhile, on the planet below, the remaining landing party is suffering through increasing cold. Attempts to beam heaters and other support devices produce only non-functional duplicates. Kirk speaks to Sulu in the Enterprise's briefing room, trying to reassure his helmsman, while growing more and more unsure of his command abilities. Spock cuts in and tells Sulu to hold on for just a little while longer.
Evil Kirk is screaming while being restrained on a bio-bed in sickbay, in pain from his body functions having been weakened from the duplication process. Good Kirk takes his evil self's hand, tells him not to be afraid and to use his mind, rather than his savagery. McCoy takes Kirk aside for a brandy. Kirk realizes he needs his negative side of himself back but does not want it. McCoy assures his captain that all Humans have a dark side to them and that his strength of command lies in his negative self.
Finally, Scotty and Spock believe they have isolated and repaired all the damage. Spock contacts Kirk and asks him to come down to the transporter room. An Alfa 177 canine test animal, previously split, is sent through to see if it will reintegrate. Spock and Scotty subdue the fierce canine with a hypospray. Spock and Fisher place the two canines on the transporter pad and Scotty energizes. "If this doesn't work, I don't know what will", Scotty says. The canines become one again, but it rematerializes dead from the shock from having suddenly had its two halves reintegrated.
The evil Kirk recovers in sickbay while Sulu contacts the good Kirk from the planet, just before he succumbs to the extreme cold. The good Kirk decides to release his evil half and have both of them go through the transporter, but the evil Kirk attacks and overpowers the good Kirk heading to the bridge where he orders navigator Lieutenant John Farrell to take the ship out of orbit and abandon Sulu along with the landing party, callously asserting that the landing party cannot be saved. At this point, the good Kirk appears on the bridge with McCoy where the evil one collapses under the strain. Both Kirks are taken to the transporter where he materialzes as one person again and the much more confident captain has the landing party rescued, frostbitten but alive.
- "Captain's log, stardate 1672.1. Specimen gathering mission on planet Alpha 177. Unknown to any of us during this time a duplicate of me, some strange alter ego, had been created by the transporter malfunction."
- "Captain's log, stardate 1672.9. On the planet's surface, temperatures are beginning to drop; our landing party there in growing jeopardy. Due to the malfunction of the ship's transporter, an unexplained duplicate of myself definitely exists."
- "Captain's log, stardate 1673.1. Something has happened to me. Somehow in being duplicated, I have lost my strength of will. Decisions are becoming more and more difficult."
- "Captain's log, stardate 1673.5. Transporter still inoperable... my negative self is under restraint in sickbay... my own indecisiveness growing... my force of will steadily weakening. On the planet condition critical, surface temperature is 75 degrees below zero. Still dropping."
- "Captain's log, stardate 1673.1, entered in by Second Officer Spock. Captain Kirk retains command of this vessel, but his force of will rapidly fading. Condition of landing party critical. Transporter unit still under repair."
"Can I help you, Captain?"
"Jim, will do here, Janice."
"You're too beautiful to ignore. Too much woman."
"We've both been...pretending too long."
- - Kirk's evil duplicate, seducing Janice Rand
"You can't afford the luxury of being anything less than perfect. If you do, they lose faith, and you lose command."
- - Spock, to Kirk's good duplicate
"I'm Captain Kirk. I'M CAPTAIN KIRK!!!"
- - Kirk's evil duplicate
"And what is it that makes one man an exceptional leader? We see here indications that it's his negative side which makes him strong, that his evil side, if you will, properly controlled and disciplined, is vital to his strength."
- - Spock, to McCoy
"If I seem insensitive to what you're going through, captain, understand: it's the way I am."
- - Spock to Kirk's good duplicate, as the latter begins to lose his will to command as a result of the transporter accident
"Do you think you might be able to find a long rope somewhere and lower us down a pot of hot coffee?"
"I'll see what we can do."
"Rice wine will do if you're short on coffee."
- - Sulu and Kirk's good duplicate
"Any possibility of getting us back aboard before the skiing season opens down here?"
- - Sulu
"He's like an animal. A thoughtless, brutal animal. And yet it's me. Me!"
- - Kirk's good duplicate, on his evil counterpart
"We all have our darker side. We need it! It's half of what we are. It's not really ugly. It's Human."
- - McCoy, to Kirk's good duplicate
"The intelligence, the logic. It appears your half has most of that. And perhaps that's where man's essential courage comes from."
- - McCoy, to Kirk's good duplicate
"He's dead, Jim."
- - McCoy, on the test animal
"Being split in two halves is no theory with me, doctor. I have a Human half, you see, as well as an alien half, submerged, constantly at war with each other. Personal experience, doctor. I survive it because my intelligence wins over both, makes them live together."
- - Spock, on merging the two Kirks
"The animal part of me came to your cabin. He even scratched me to make us look more alike. I'd like a chance to explain it to you. You don't mind if I come to your cabin later?"
- - Kirk's evil duplicate, seducing Janice Rand again by pretending to be his good counterpart
"Can half a man live?"
- - Kirk's good duplicate, to his evil counterpart on the bridge
"I want to live!"
- - Kirk's evil duplicate
"I've seen a part of myself no man should ever see."
- - Kirk to McCoy, after the successful reintegration
"The ... impostor had some ... interesting qualities, wouldn't you say, yeoman?"
- - Spock, to Rand
- Story outline by Richard Matheson: 4 April 1966
- Revised story outline: 22 April 1966
- First draft teleplay by Matheson: 25 April 1966
- Revised first draft teleplay: 19 May 1966
- Second draft teleplay: 31 May 1966
- Revised teleplay by John D.F. Black: 6 June 1966
- Final draft teleplay by Gene Roddenberry: 8 June 1966
- Additional revisions: 11 June 1966, 15 June 1966
- Filmed: 14 June 1966 – 22 June 1966
- Score recording: 14 September 1966
- Original airdate: 6 October 1966
- First UK airdate 13 April 1970
Story and production Edit
- Writer Richard Matheson's main influence on writing this episode was Dr. Jekyll and Mr. Hyde, as he envisioned Robert Louis Stevenson's classic story put in a science fiction context. He eventually came up with the idea of the transporter causing a man to be split into two halves. 
- The subplot of Sulu and three other crewmembers stranded on the planet was not present in Matheson's original script, and was added in staff re-writes. Matheson did not like the idea, as he had an aversion to B-stories in general, believing they slowed stories down. He explained, "My script stayed entirely with Bill [Shatner] having this trouble of his two selves, on the ship [....] They added a whole subplot about people down on the planet, ready to freeze to death, because they have [a] transporter functioning problem [....] I stuck entirely with Bill." 
- The last two scenes of Act One are switched in order from what appears in the script. In the teleplay, Kirk and Spock learn about the assault of Janice in sickbay, then head to the transporter room, where they are faced with the discovery that the transporter is creating duplicates. The act ends with Scotty suggesting, "We don't dare beam up the landing party. If this should happen to a man..." and Kirk exclaiming, "Oh, my God!" In the episode itself, the sickbay scene follows the one in the transporter room, and the act ends with Spock declaring, "There's only one conclusion – we have an impostor aboard." Director Leo Penn was known to reorganize scenes when he deemed them to be more dramatic in a different order from what was scripted. 
- In the final draft and the revised final draft of this episode's script, McCoy mused that part of "the Human condition" was having "an enemy within."
- Grace Lee Whitney once recounted that, while shooting the scene when a distraught, tearful Janice Rand accuses Captain Kirk of trying to rape her, William Shatner slapped her across the face to get her to register the proper emotion.  As they shot the rape scene days earlier, Whitney couldn't get into the same emotion successfully, and it was Shatner's "solution" to the problem. (The Longest Trek: My Tour of the Galaxy, p. 94)
Props and sets Edit
- The sensor device used by Scott to scan the ore on Fisher's uniform appears to be a modified Nuclear-Chicago Model 2586 "Cutie Pie" radiation detector.  This Feinberger reappeared in "The Naked Time", "The Doomsday Machine", and "Obsession".
- In this episode we get to follow Kirk behind the large engine room machinery components in the first trip to the engineering deck (which dialogue identifies as being in the lowest parts of the ship). To allow this to happen, the new set had to be temporarily expanded to hide the sound stage beyond it. After the double is rendered unconscious by the first neck pinch in the series, the quickly-assembled wall behind the three characters can be observed to have a very rough edge where it meets the floor. Pieces of sets that were designed to be added and subtracted easily were called "wild." Although Kirk pursues Ben Finney into these components in "Court Martial", this is the only time we get to see the space behind them. The view of the tubed structures behind the grille was a forced perspective set. The tubed machinery appears to be many dozens of meters long, but this is an illusion created by making each vertical piece much smaller than the one in front of it. Diminishing numbers were later printed on the tubes immediately behind the grid to add to the illusion. In episodes where the engines were under stress, lighting effects were used inside the tubed-machinery room. The set was extensively remodeled between the first and second seasons.
- A shot, showing two extras (Frank da Vinci and Ron Veto) in red technician jumpsuits (and Veto holding the aforementioned "Cutie Pie" prop) in the engineering set was filmed, but cut from the episode. It was probably filmed as an insert shot for scenes at engineering. 
- The gauzy, red-bordered triangular set piece behind which the evil Kirk emerges briefly in engineering during the hunt scene appears to have been left over from the early briefing room as seen in "The Cage" and "Where No Man Has Gone Before".
- 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 "The Devil in the Dark".
Special effects Edit
- The showering phaser effect used when Sulu heats the rock is never used again. Just before he sprays the rocks, Sulu also appears to be fitting his hand phaser into its pistol mount – again, a maneuver that is never repeated.
- There are two split screens used: after Kirk's double is neck-pinched and, in sickbay, when he takes the hand of his counterpart. All other instances of the two Kirks appearing in the same shot were done using doubles.
- At the start of the episode when Kirk is beamed up from Alfa 177, both he and his evil counterpart are missing the Enterprise insignia on their uniforms. Lieutenant Farrell is also missing his insignia at some points during the episode (and also in a shot recycled from this episode in "Mudd's Women"). The Star Trek Compendium suggests that the insignia were removed every time the uniforms were cleaned (union rules required them to be cleaned daily), and during production of this episode, someone forgot to put them back on Kirk and Farrell's uniforms.
- The first season version of the captain's wraparound tunic was created for this episode, with the original purpose of differentiating Kirk from his double. It reappears in "Charlie X" and "Court Martial", and in Kirk's briefcase in "This Side of Paradise". The tunic was constructed of wool crêpe fabric, in contrast to the velour of the standard duty tunics.
- Although Nichelle Nichols does not appear in this episode, her voice is heard on the intercom in several scenes.
- This episode marks the first time on screen that Kirk is duplicated in some form or fashion. This repeats again through "What Are Little Girls Made Of?", "Whom Gods Destroy", and Star Trek VI: The Undiscovered Country.
- Spock's log entry in this episode calls himself "Second Officer Spock", however, in "Court Martial" the computer lists him as "First Officer Spock" and from then on is referred to as a "first officer" until his return in Star Trek: The Motion Picture as simply science officer.
- This was the first episode to show the Vulcan nerve pinch, as well as the first time McCoy says "He's dead, Jim." Leonard Nimoy objected to the script's directive that Spock "kayoes" the evil Kirk on the head, so he improvised the neck pinch on the spot and demonstrated it on William Shatner for director Leo Penn. (Star Trek Encyclopedia) The script's original directive survives to this day in the James Blish adaptation of this episode (in the book Star Trek 8) as Blish only had access to the scripts and not to the finished episodes.
- The transporter was depicted as the only mode of transport between a planet and the ship because this episode was written and filmed before the existence of the hangar deck and shuttlecraft were established. (Star Trek Encyclopedia)
- The phaser that "evil" Kirk steals from Wilson outside his cabin is clearly a type 2 phaser. When "good" Kirk encounters him in engineering, in the long shots, "evil" Kirk is seen brandishing a type 1 hand phaser. However, in the close-ups, he's back to carrying a type 2 phaser.
- In the sequence of aired episodes, this is the first episode where we see or hear the new middle initial for James Kirk. "Captain James T. Kirk" is briefly visible as the negative-Kirk enters Kirk's quarters. The initial was first spoken in "Mudd's Women", but that episode aired after "The Enemy Within".
- In the latter part of the scene where the two Kirks appear together on the bridge, a close-up shot of the Negative Kirk shows the scratches on the right side of his face, although wider shots (and all earlier scenes) showed they were on the left side. This was due to the shot being reversed during editing. Director Leo Penn and cameraman Jerry Finnerman mistakenly filmed the close-up out of axis, breaking the 180-degree rule, and editor Fabien Tordjmann could only help by reversing it, hoping the audience won't notice the resulting continuity error. (These Are the Voyages: TOS Season One)
- A reaction close-up shot of Spock on the bridge is recycled from "The Naked Time". The same shot was used again in "The City on the Edge of Forever".
- In the novel Foul Deeds Will Rise, the duplication witnessed here is documented as 'the Alfa Effect', with another character duplicating the effect to give herself an alibi for various murders (One of her appears in public while the other commits the crimes), claiming to have adjusted the balance so that both duplicates share the same personality traits as opposed to the imbalance witnessed here (although the duplicates do demonstrate a divergence later, with one being more violent while the other accepts their failure).
- After the two Kirks are rejoined, the (whole) Kirk refers to his "evil" side as "the imposter", although it had been made clear that each half contained separate characteristics of the man himself, and there is every reason to suppose that the whole Kirk retained memories from both "halves". Clearly the "evil" Kirk was no more an imposter than the "good" Kirk.
- Actress Grace Lee Whitney was very unhappy about the last scene of this episode, in which Spock asks Yeoman Rand, if "the impostor had some very interesting qualities, wouldn't you say, yeoman?". In her autobiography, she wrote: "I can't imagine any more cruel and insensitive comment a man (or Vulcan) could make to a woman who has just been through a sexual assault! But then, some men really do think that women want to be raped. So the writer of the script (ostensibly Richard Matheson - although the line could have been added by Gene Roddenberry or an assistant scribe) gives us a leering Mr. Spock who suggests that Yeoman Rand enjoyed being raped and found the evil Kirk attractive!" (The Longest Trek: My Tour of the Galaxy, p. 95.
- Despite this, Whitney enjoyed this episode. "I love "The Enemy Within" because it gave me a chance to really react and act with Bill Shatner. I love it! I loved the whole concept of him breaking into two characters because that really was what Kirk and Rand were about. There were two sides of Kirk and two sides of Rand. Rand was there to be of service to him but she was also in love with him. But she knew she mustn't go over-go the boundaries." (These Are the Voyages: TOS Season One, p. 159)
- James Doohan stated that he thought William Shatner's performance in this episode was "pretty okay." (Beam Me Up, Scotty, p. 132)
- Director Leo Penn also praised Shatner's performance. "William Shatner's a very good actor and gave a very good performance... I had a good time on that show." (These Are the Voyages: TOS Season One, p. 159)
- Richard Matheson elaborated, "I thought Bill Shatner was brilliant. I loved what he did. He carried the whole thing. I was a little sorry that Roddenberry put so much emphasis on the crew being stuck on the planet [....] But I liked it and I was very satisfied with the production value." (These Are the Voyages: TOS Season One, p. 159)
Video and DVD releasesEdit
- Original US Betamax/VHS release: 28 February 1985
- Original UK VHS release (two-episode tapes, CIC Video): Volume 3, catalog number VHR 2244, release date unknown
- US VHS release: 15 April 1994
- UK re-release (three-episode tapes, CIC Video): Volume 1.2, 8 July 1996
- Original US DVD release (single-disc): Volume 2, 17 August 1999
- As part of the TOS Season 1 DVD collection
- As part of the TOS Season 1 HD DVD collection
- As part of the Star Trek: Fan Collective - Alternate Realities collection
- As part of the TOS Season 1 Blu-ray collection
Links and referencesEdit
- George Takei as Sulu
- James Doohan as Scott
- Edward Madden as Fisher
- Garland Thompson as Wilson
- Jim Goodwin as Farrell
Uncredited co-stars Edit
- Frank da Vinci as Vinci (scene deleted)
- Eddie Paskey as Leslie
- Ron Veto as Harrison (scene deleted)
- Unknown actors as
Stunt double Edit
- William Blackburn as the stand-in for DeForest Kelley
- Frank da Vinci as the stand-in for Leonard Nimoy
- Jeannie Malone as the stand-in for Grace Lee Whitney
- Eddie Paskey as the stand-in for William Shatner
abort control circuit; Alfa 177; Alfa 177 canine; autopsy; "base cycle, stunning force"; body function panel; "Bones"; cabin; coadjutor engagement; coffee; decontamination; dizziness; Earth; engineering; exposure; frost; frostbite; geological technician; hand phaser; hotline; impulse engine; leader circuit; logic; magnetism; make-up; microtapes; mirror; ore; postmortem; protoplaser; power generator; rape; rice wine; room service; rope; Saurian brandy; ship's manifest; shock; skiing; survival training; synchronic meter; thermal heater; tranquilizer; transporter; transporter circuit; transporter technician; transporter unit ionizer; vacation; velocity balance; Vulcan nerve pinch; willpower
- "The Enemy Within" at StarTrek.com, the official Star Trek website
- "The Enemy Within" at Memory Beta, the wiki for licensed Star Trek works
- "The Enemy Within" at Wikipedia
- "The Enemy Within" at MissionLogPodcast.com, a Roddenberry Star Trek podcast
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