Original air date: October 6, 1966
Kirk, Sulu and some unusually long lived Red Shirts are collecting specimens from Alfa 177 when someone falls down a hill and gets a boo-boo. He's beamed up, along with a strange, magnetic ore that he picked up in his fall. Shortly after, Captain Kirk beams up, feeling a little woozy. Scotty leads him away, even as Kirk warns him not to leave the transporter room unattended. What beams up next is... Captain Kirk! You can tell it's an evil Kirk! He's wearing eye liner and sweating like a pig!
So now, Kirk's got a doppelganger running about acting more like Captain Morgan than Captain Kirk. No one dares use the transporter now, so Sulu and company are left behind on a planet that gets well below 0 at night. And it seems that whatever happened to Kirk also happened to a little canine creature. One's a sweet little lap dog, the other... well, ever see that Tom and Jerry cartoon called "The Cat's Me-Ouch!"?
The Tropes Within:
- Absentee Actor: Uhura doesn't appear, although her voice is heard on the intercom.
- Attempted Rape: Poor Janice is subjected to this by Evil Kirk.
- Balance Between Good and Evil: The aesop is that a person can't function without both the light and dark sides. Without the light, Evil Kirk is unrestrained and violent; without the darkness, Good Kirk is impotent.Spock: 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.
McCoy: (to Good Kirk) We all have our darker side. We need it! It's half of what we are. It's not really ugly. It's Human.[...] The intelligence, the logic. It appears your half has most of that. And perhaps that's where man's essential courage comes from.
- Braving the Blizzard: Mr. Sulu and several others get trapped on the planet the Enterprise is orbiting. As night comes on, the wind kicks up and the temperature falls dramatically. Due to the malfunction, any heaters transported down are rendered useless, and the away team is forced to use their phasers to superheat rocks in order to stay warm enough to survive.
- Clear My Name: Certainly important to Good Kirk.
- Color-Coded for Your Convenience: Evil Kirk wears the yellow command uniform. Good Kirk wears his casual green shirt. That is, until Evil Kirk realizes he can (temporarily) fool people by changing his shirt.
- Dirty Coward: Evil Kirk lacks Good Kirk's courage (see Villainous Breakdown).
- Early Installment Weirdness:
- It's a bit weird to see Spock call himself "half human, half alien," when for the bulk of the series he clearly identifies as Vulcan.
- Sulu could have been brought aboard had they thought to use the shuttlecraft. The only reason they didn't use it is because they hadn't built the shuttlecraft sets and models yet.
- As with a few of the other early episodes, several of Kirk's captains logs are done in the past tense rather than present tense.
- Enemy Within: Well, duh! Look at the episode's title!
- Enemy Without: How it comes to be.
- Evil Is Hammy: Good Lord. Evil Kirk makes all of Shatner's other performances look subdued.Evil Kirk: I'm Captain Kirk! I'm Captain Kirk! I'M CAPTAIN KIRK! IIIII'M CAPTAIN KIRRRRRK!!!
- Evil Me Scares Me: "I've seen a part of myself no man should see."
- Evil Twin: Created by transporter accident. This is a rare case where the evil twin isn't an imposter, but actually is the real person (albeit the negative, disagreeable side of that person).
- First-Name Basis: Evil Kirk tells Yeoman Rand to call him Jim, as he calls her Janice.
- Gallows Humor: Sulu cracks a few jokes about just needing a coffee when it's a very real possibility they could die from cold.
- Good Eyes, Evil Eyes: Evil Kirk wears eyeliner and his eyes are always narrow and shifty.
- Good Is Impotent: Evil Kirk has been given all of Kirk's willpower, determination, and aggression, and left without these traits Good Kirk is rather meek, indecisive, and passive. But it actually is played with a little, as Good Kirk has been saddled with Kirk's courage, while Evil Kirk at heart is afraid and falls into a useless panic at the thought of losing his individual existence, while the Good side can calmly accept it.
- Guyliner: Evil Kirk wears it, as per the Excessive Evil Eyeshadow trope. He also puts on some make-up in attempt to hide the scratches Rand put on him.
- He's Back!: Kirk's halves are put back together and it's obvious he's survived the process, but the real "He's Back!" moment comes when he decisively says "Get those men aboard fast!"
- He's Dead, Jim
: For the first time in the series! After they attempt the re-merging with the creature, McCoy and Spock examine the limp form that beams up.Spock: It seems the shock was too much.
McCoy: He's dead, Jim.
- I Need a Freaking Drink:
- Evil!Kirk demands Saurean brandy when he enters sick bay. Later, Bones decides that both he and Good!Kirk need it.
- Sulu cracks a few jokes about needing coffee (due to the freezing temperatures of the planet), then says that sake will do as well.
- Idiot Ball: Who exactly thought it was a good idea to have Yeoman Rand questioned about her attempted rape by the accused perpetrator? The same people who thought it was a good idea to let the accused walk around after being identified by an eyewitness. Though Good Kirk pretty quickly proved it wasn't him, he has no scratches on his face. This being Star Trek, everyone is immediately convinced that something substantially weirder is going on.
- Jekyll & Hyde: A transporter malfunction splits Kirk's good and evil sides.
- Literal Split Personality: Kirk of this episode is a famous example. It is learned that the "evil" side proved to be the side with the strength to make tough decisions, proving that both halves are needed for the whole to work. And the seemingly meek, passive "good" side turns out to have more courage than the other, whose angry defiance hides terror of losing independent existence."Can half a man live?"
- Mundane Utility: Sulu uses a phaser to heat up some rocks for warmth. Beginning a long, proud Trek tradition, fully in fitting with its themes, that phasers are as much tools as weapons.
- Must Have Caffeine: Sulu asks if it's possible for them to send down a pot of coffee. Possible, he just wants something hot. He would've settled for sake.
- OOC Is Serious Business: Never has it been more serious! And on both sides: Good Kirk lacks the command presence and decisiveness he's previously demonstrated and which is necessary for The Captain, Evil Kirk lacks empathy, courage, or any real impulse control. The trick is not to figure out which Kirk is which, but that they're both equally not "real" Kirk.
- Out-of-Character Alert: Kirk is split into his good and evil sides by a transporter accident, which leaves several of the Enterprise crew stranded on a hostile planet. Spock feels a bad vibe when the evil Kirk, passing himself as the good one, walks onto the bridge. Then he declares that the men can't be saved and orders the ship to leave orbit, at which point Spock knows it's not the real one - since when would James T. Kirk leave his crew to die?
- Plot Hole:
- Why doesn't Kirk send a shuttlecraft to collect the stranded men? (The Doylist answer is because they hadn't finished building the shuttlecraft set.)
- Why doesn't the Enterprise crew beam down some blankets? It's not like bedding can get split into Good and Evil. The heaters that were beamed down didn't work, but this shouldn't apply to blankets. Or coffee, for that matter.
- They could have even beamed the characters up and confined the resulting duplicates until the problem was fixed.
- The Power of Hate: When Kirk gets split into Good Kirk and Evil Kirk, Good Kirk is barely able to function because, as Bones points out, he needs the power of hate as well as love.
- Ridiculously Cute Critter: Sulu finds something that looks like a mash up of a cocker spaniel, a unicorn and a baby dragon with some screwy looking antenna. And it's flippin' adorable! (When its evil half isn't trying to eat your face, that is.) What a pity that it dies in the end.
- Sarcasm Failure: See Gallows Humor. As the (admittedly improbable) cold gets to the stranded crew members, Mr. Sulu's last communication to the Enterprise is laconic and quiet.
- Shadow Archetype: The good-yet-indecisive Kirk and his evil-yet-effective twin: "I have to take him back... inside myself. I can't survive without him. I don't want him back. He's like an animal, a thoughtless, brutal animal — and yet it's me. Me." Really though, both the good and evil Kirk are Shadow Archetypes to the real Kirk; he wouldn't want to be either one of them.
- Shirtless Scene: Shortly beaming up, Good Kirk feels a sudden urge to go change his shirt. The ladies (and Mr. Spock) get some eye candy, and there's a reason for the sudden Color-Coded for Your Convenience.
- Society Marches On: Evil Kirk tries to rape Yeoman Rand. She later recounts the incident for Good Kirk, Spock and McCoy, displaying a very '60s attitude about it ("I don't want to get you into trouble. I wouldn't even have mentioned it.") while being in tears. And this is while she is unaware that there are two Kirks running around! Sadly this, among other reasons, are why rape survivors often don't report it even as of 2020.
- Take a Third Option: Spock explains how he uses this to live. His human and Vulcan natures are constantly in conflict, but he uses his intelligence to keep both in line and make them work together.
- Tantrum Throwing: Evil Kirk throws a fit when he can't get his way.
- Technobabble: Spock's explanation of how the transporter was repaired comes off as this.
- Understatement: Before beaming up, Kirk tells Sulu that the temperature on the planet gets down to some ridiculously low arbitrary temperature at night. Sulu replies, "That's nippy."
- Villainous Breakdown: Evil Kirk finally gives up when he breaks down, sobbing, "I don't wanna die!""I don't wanna go back. I wanna LIIIIIIVE!!!!"
- Warring Natures: Spock claims that his human side and his "alien" side are constantly doing this.
- What the Hell, Hero?: McCoy gives this to Spock when he uses Kirk's situation to coolly analyze the roles of good and evil in human nature. Spock doesn't back away from the accusation, but does offer an apology of sorts to Kirk for his seeming to be uncaring.
- Whole Plot Reference: Richard Matheson's main influence on writing this episode was The Strange Case of Dr. Jekyll and Mr. Hyde, as he envisioned the 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.
- With All Due Respect: Spock tells Kirk that he doesn't have the luxury of indulging his conscience:Captain, no disrespect intended, but you must surely realise you can't announce the full truth to the crew. Youre the Captain of this ship. You havent the right to be vulnerable in the eyes of the crew. You cant afford the luxury of being anything less than perfect. If you do, they lose faith, and you lose command.
- Writers Cannot Do Math: No matter what scale you use, the temperatures given for the planet's surface mean Sulu's team would have frozen to death before the episode is even halfway over.