Original air date: November 1, 1968
Instead of the usual trio, it's Kirk, Chekov, Bones and an unusually long lived Red Shirt who beam down to Beta XII-A, a planet of rocks and pink trees, to answer a distress beacon. While Kirk laments the hundreds of men, women, and children who have been murdered (mysteriously, without leaving any bodies or building wreckage) Spock reports a Klingon ship in orbit, apparently in distress. A small group of Klingons, led by Commander Kang (no, not THAT Kang) and his wife Mara (the first female Klingon to be aired thus far) beam down and accuses Kirk of attacking his ship and killing his crewmen. Kirk denies doing such a thing and brings up his counter accusation. Chekov accuses the Klingons (again, he calls them "Cossacks") of murdering his heretofore unmentioned brother, Piotr. Kang tortures Chekov and threatens to do more if Kirk does not surrender his ship to the Klingons. Kirk pretends to surrender, but sends a secret signal to Spock that only the Enterprise crew be beamed aboard, with the Klingon crew kept in stasis until security can handle them. Kang and his crew are detained in the lounge while a mysterious Anti-Tinkerbell looms nearby.
Tempers flare as Irrational Hatred overrides good sense. Klingons and Federation had always shared an enmity, but now it's getting out of hand! Boing! The chess set, some pool cues and the phasers have all turned into swords! Rather than question this turn of events, everyone decides to start swashing bucklers (yes, it is that way round).
Day of the Tropes:
- Attempted Rape: Chekov tries to rape Mara, Kang's wife, while under the influence of the alien. Luckily, Kirk arrives and knocks him out before he can get too far.
- Battle Couple: Kang and his wife Mara. They serve on the same ship together.
- Bloodless Carnage: Though swords are swung about and even hit a few people, we don't see any blood. The energy being is keeping the injured alive so they can fight more, but this still seems a bit odd.
- Bridal Carry: Kirk does this to Chekov after knocking him unconscious.
- Character Development: Kirk gets some that sticks. While he remains pissed off at the Klingons, even moreso after his son is killed, he's finally on the side of diplomat now, discarding the good little soldier who follows rules.
- Color Motif: In this episode where the theme is aggression, red lighting is used a lot.
- Covert Distress Code: When Kirk calls the Enterprise and asks for a wide-field beam-up, he presses a button on his communicator that lights up a panel on the big chair. Spock gets the message, and Scotty sees to it that Kirk and his officers materialize first while holding the Klingons in suspension until a security team shows up.
- Dangerous Forbidden Technique: Intraship beaming (using the transporters to get to another part of the ship). Apparently, the risk of Tele-Frag is much higher at extreme close range (though they get this flaw ironed out in about 100 years, where it is explained in supplemental materials as needing extra precision for a moving target).
- Dissension Remorse
- After an argument on The Bridge nearly leads to an all-out fight.Kirk: (to Spock) STOP IT, YOU HALF-HUMAN what am I saying? What are we doing to each other?
- Later, when the main crew realize how the Energy Being had manipulated them:McCoy: Gentlemen, if we are pawns, you're looking at one who is extremely sorry.
Spock: I understand, Doctor. I, too, felt a brief surge of racial bigotry. Most distasteful.
- After an argument on The Bridge nearly leads to an all-out fight.
- Easily Thwarted Alien Invasion: An alien powerful enough to destroy a Klingon battlecruiser, transmute matter and control the minds of hundreds of beings simultaneously takes control of the Enterprise. How do the humans and Klingons get rid of it? By laughing at it. Seriously.
- Emotion Eater: The big glowy entity that feeds off of negative emotions and is turned off by good ones. Kirk manages to get rid of it by laughing with a few Klingons.
- Energy Being: Again with the Klingons? Again with the Energy Being! Kirk and co. fight these more often than the Klingons!
- "Everybody Laughs" Ending: Invoked—in a show of good spirits, everyone laughs together to drive away the Energy Being. Kang's hearty slap on Kirk's back seemed a little stronger than need be, though.
- Evil Virtues: Kang admires Chekov's loyalty, even as he tortures him.
- Exact Words: "I'll beam you aboard the Enterprise .... once there...no tricks."
- Fake Memories: If the being doesn't think the hate is strong enough, it will season it with some unhappy memories (such as Chekov believing he had a brother who was killed in a Klingon attack). It's quite possible that the Federation colonists of Beta XII-A never even existed.
- Fantastic Racism: The entity deliberately stirs this up as part of its MO. The Enterprise crew — who have never liked Klingons, admittedly, but are trained to seek a peaceful solution in preference to conflict — suddenly begin developing a murderous hatred toward them, viewing them as nothing more than animals. In addition, bigotry begins to emerge between the crew, with Scotty yelling at Spock to keep his Vulcan hands off him and calling him a "green-blooded half-breed", and Spock replying coldly that he has not thoroughly enjoyed serving with humans. He later comments that experiencing these feelings was "most distasteful".
- Forced to Watch: Kang threatens to torture Kirk's crew while Kirk watches. Betcha thought he was gonna go for the Red Shirt first!
- Get Out!: Once the humans and Klingons stop fighting, Kirk tells the entity that it's no longer welcome aboard the Enterprise.Kirk: Get off my ship. You're a dead duck here. You're powerless. We know about you, and we don't want to play. Maybe there are others like you around. Maybe you've caused a lot of suffering, a lot of history, but that's all over. We'll be on guard now, ready for you, so ship out! Come on! Haul it!
McCoy: Yeah, out already!
(both men laugh)
Kang: Out! We need no urging to hate humans. But for the present, only a fool fights in a burning house. OUT!
(everyone laughs uproariously at the entity as it slinks off)
- Hate Plague: An Energy Being that feeds on hate brings the Federation and the Klingons, who are trying to abide by the peace treaty, into conflict. It goes as far as implanting Fake Memories so that the manipulated will have an extra source of conflict. An interesting part of this trope in Star Trek is that those who are killed are somehow brought back to life with their fatal wounds healed to fight again. Once they all figure it out the creature is repelled from the ship by laughter. Lots and lots of laughter.
- Hell Is War: The being pits the crews of the Enterprise and a Klingon ship against each other, balances the odds by locking most of the Enterprise crew below decks, gives them primitive weapons to deal the most damage, and heals any wounded. This allows the being to live forever off the crew's hate, as they are locked in battle forever, immortal. Luckily, Kirk figures this out before it happens.
- Humans Are Bastards: Mara thinks that the Federation has death camps, performs atrocities and will torture the captured Klingons for information.
- Hungry Menace: Like Redjac from "Wolf In The Fold" fed on fear, this being feeds on hate.
- I Have Your Wife: Kirk tries to bluff Kang into thinking that Kirk will kill Mara, Kang's wife. Kang doesn't fall for it.
- Info Drop: Appropriately for a pro-peace episode, this one slips in some sympathetic background info on the Klingon empire. According to Kang and Mara, the empire pursues an expansionist policy because the Klingons' territory is relatively resource-poor.
- Involuntary Battle to the Death: The hate feeding entity goads the Klingons and Enterprise crew into one.
- It's Personal: The Energy Being feels that Chekov's strong dislike of Klingons needs to be seasoned with a personal vendetta. Lt. Johnson bounces back quickly for a Red Shirt, but decides the Klingons still have to pay for what they did to him.
- Just Ignore It: The entity that feeds on hatred is weakened when a truce is made between Federation and Klingon combatants, then driven off when the two sides start laughing at it.
- Large Ham: Everyone under the alien's influence—except for Spock, who instead has a bout of Tranquil Fury.
- Misdirected Outburst: The crew's increasingly hostile attitude leads to quite a few of these being exchanged. Eventually they reach the point where Kirk realizes that something is seriously wrong, which leads to figuring out the problem and its solution.
- Moment of Weakness: Invoked but rejected. Spock suggests that the hostile behavior might be a result of stress; Kirk responds that they've been under stress before and it never made them turn on each other.
- My Country, Right or Wrong: Kang's attitude towards the Klingon race.
- My God, What Have I Done?: Kirk has two such moments. One when he calls Spock a "half-human" and one when he beats Chekov senseless.
- No Such Thing as H.R.: Bones' and Spock's good-natured bickering becomes overheated in this episode.
- Not Afraid of You Anymore: Kirk tells the entity that it may as well leave because no one on this ship was going to feed it.
- No Conservation of Energy: The Emotion Eater is able to transmute metal into phaser-proof alloys, transform said phasers into swords, propel the Enterprise to Warp Nine and hold her together at that speed - all on the emotional energy of a handful of combatants. That's some powerful hate there.
- Not What It Looks Like: Kang sees Mara's torn tunic and growls "I see why the human beast did not kill you," implying that he thinks she was raped. Mara insists that Kirk didn't harm her and is telling the truth about the situation.
- O.O.C. Is Serious Business: So many out-of-character freak outs! All courtesy of the alien, of course.
- Chekov has expressed a strong dislike of Klingons, calling them "Cossacks" in "The Trouble With Tribbles", yet Scotty was able to talk him down (until he threw some punches himself.) Here, even Kirk has trouble holding back the enraged ensign.
- Kirk himself slams his Heterosexual Life-Partner for being a Half-Human Hybrid.
- Uhura is usually serene, showing only mild concern when things go wrong with communications. Her hysterical freak out is combined with a wild accusation at the Klingons.
- Bones is known for the occasional emotional outburst, but his militant demand for the death of the Klingons is bit much.
- Scotty all-out accuses Kirk of jeopardizing The Federation for not letting the Klingons die in the first place. He also calls Spock a "green-blooded half-breed" and a "freak".
- Spock says in a dry monotone that he has never much enjoyed working with humans, which is a screaming rage by Spock standards.
- Averted with Sulu, who is apparently the only one who's never affected by the energy being.
- Outgrown Such Silly Superstitions: Kirk tells Kang, "Go to the Devil!" (Couldn't say "Go to Hell" on TV in the 60's.) Kang replies, "We [Klingons] have no Devil... but we are very familiar with the habits of yours." Cue use of torture. In later series, it would be revealed that Klingon mythology does have a character called Fek'lhr who is much like the Judaic version of Satan, i.e., not necessarily evil, just having an unpleasant responsibility. Klingons very much have an equivalent of Hell, known as Gre'thor, of which Fek'lhr is the guardian. It's eventually clarified that Fek'lhr brings the souls of the dishonored to Gre'thor, and is absolutely not a corrupter like the human concepts of Satan - it would make him more like a combination of Charon and Cerberus. So while "go to the Devil" means nothing to a Klingon, "go to Fek'lhr" would've been a grave insult indeed.
- Parenthetical Swearing: Scotty says the line "Keep your Vulcan hands off me!" with a very specific emphasis on the word 'Vulcan'.
- Rape Discretion Shot: Chekov tearing Mara's clothes isn't actually shown, just heard. Even so, the obviousness of his intentions is pretty shocking for the time period.
- Rape Is a Special Kind of Evil: Chekov decides killing's too good for Mara. Luckily, Kirk steps in just in time.
- "The Reason You Suck" Speech: Scotty, of all people gives Spock a BLISTERING one. But he isn't himself.
- Kirk, Bones, and Kang serve the sadistic entity a really nasty one, each telling it to Get Out!, and underscored with very hearty laughter by Enterprise and Klingon crews.
- Red Shirt: Johnson takes a sword to the chest. If not for the alien, he'd be dead.
- Red Shirt Army: The only actual casualties are the majority of Kang's crew, killed by the alien. Assuming that they even existed...
- Resurrection Revenge: A Red Shirt is resurrected by an Energy Being because it wanted him alive to be angry with and fight the Klingons.
- Rivals Team Up: Kirk has to convince the Klingons who are trying to take over the ship to work together against an alien presence who is feeding off of their emotions.
- See You in Hell: Couldn't say that on TV in the 60's. Had to stick with "Go to the Devil."
- Sheathe Your Sword: The only way to win against the alien entity is to throw down their swords and refuse to fight.
- Smack on the Back: At the end of the episode where the characters are laughing together to drive out the alien, Kang slaps Captain Kirk on the back so hard that he's staggered.
- Standard Female Grab Area: Kirk uses it to capture Mara and keep her docile. Apparently even a Klingon woman can be completely incapacitated just by holding her arm.
- Stock Footage:
- Suspiciously Similar Substitute: Like Koloth in "The Trouble with Tribbles", Kang was made as one for Kor from "Errand of Mercy", because John Colicos was unavailable yet again.
- Talk to the Fist: The first thing that Kang does when he beams down to the alien planet is punch Kirk. Once they're on the Enterprise, Kirk returns the favor.Kirk: And before I put you in the brig, there's a little something I owe you. (punches Kang)
- Unwitting Pawn:
- Spock concludes that this is what the Enterprise crew and the Klingons have become to the Energy Being.
- Kirk specifically calls Kang a pawn in the final sequence, trying to convince him to throw down his weapon and end the fighting.
- The X of Y: The method used to name this episode.
- Wham Line: When Kirk explains to Sulu that Chekhovs apparent hatred of Klingons stems from the death of his brother Pyotr, Sulu informs Kirk that Chekhov is an only child. This is one of the earliest signs Kirk notices that something unusual is happening.
- Worthy Opponent: Kang.
- You Fool!: Kirk has just explained to the Klingon captain Kang that the Enterprise is under the control of a creature that feeds on hate and wants the Klingons and humans to fight for its entertainment for the rest of eternity. Kang decides to fight Kirk anyway, at which point his wife Mara exclaims "You fool!". Later, Kang himself admits "Only a fool fights in a burning house."
- You Killed My Brother: Why Chekov is so pissed at the Klingons—except he's an only child.