The planet of Gideon has refused anything to do with the United Federation of Planets until recently. The council has agreed to allow a delegation of one...one Captain James T. Kirk. Kirk has himself beamed down to the planet only to find himself beamed aboard his own starship, sans crew. Where is everybody? Kirk searches everywhere, hails everyone he can think of. His voice over the intercom reverberates off the walls of empty rooms. Kirk searches until he finds a rather dippy blonde in sparkly blue and purple PJ's dancing by herself in the corridors. Oh, Donna! No, actually [[GirlOfTheWeek her name is Odona.]] She's not sure where she's from, just that it was so crowded it made a [[TheWho Who]] concert look tranquil. It isn't long before Kirk is BoldlyComing. (You can bet they didn't go into that room to play Parcheesi!) Spock, meanwhile, is playing bureaucratic ping-pong for permission to search for the missing captain.

!!!Tropes for this episode include:

* AbusiveParent: Subversion. Hodin is quite willing to make his daughter suffer and die from meningitis. However, she volunteered to do this for [[HeroicSacrifice the good of the many.]]
* AdultFear: Kirk wakes up on an empty ''Enterprise'', all the crew members with whose safety he has been entrusted gone without a trace or any clue to what happened to them.
* AMillionIsAStatistic: Kirk refuses the let dying the person he contamined himself, but he lets this person spreading the disease to deliberately killing a lot of people.
* AssInAmbassador: Hodin is quite good at prolonging a crisis and insulting Scotty while he's at it.
* BerserkButton: Do not even hint to Scotty that his equipment is faulty. (Mind out of the gutter! They're talking about the transporter!)
* BrokenAesop: Genocide is ok when the world is overpopulated and people are unhappy about being so dang healthy all the time.
* CannotKeepASecret: Someone in Starfleet, since the Gideon government has access to a lot of useful information about the Enterprise and her Captain.
* CurseCutShort: Scotty bites his tongue before insulting the Gideon council before begrudgingly referring to them as "gentlemen".
* DyingDeclarationOfLove: Odona makes one to Kirk. Her passions cool when she realize she's not going to die after all, but has the potential to make many others sick so people can get to dying so everyone can be happy.
* DepopulationBomb: Kirk is kidnapped by a vastly overpopulated planet who wants to use germs in his blood to drop a Depopulation Bomb on ''themselves''. This scheme involves a large amount of FridgeLogic, when one wonders where they found the space to construct a full-scale replica of the interior of the ''Enterprise''. And how they got the specs for the ''Enterprise''. And why they bothered to build it at all when they could have just knocked Kirk out and taken some of his blood right after he beamed down without bothering to trick him. And...
* DistractedByTheSexy: Kirk is going mad with worry until Odona comes along. One germ swapping kiss followed by an off scene lay, and he's back to worrying about them.
* DramaticallyMissingThePoint: Instead of using the negociations with the Federation to prepare a colonization plan, the government of Gideon decide to use the negociator's deadly germs.
* FridgeLogic: Why don't the overcrowded people just colonize some other planets?
* HeyItsThatGuy: This episode was written by Stanley Adams, better known Cyrano Jones, dealer of the one species that multiply quicker than Gideons...tribbles.
* IllGirl: Odona seeks to become one and succeeds.
* InferredHolocaust: They barely try to hide this. Odona returns to Gideon, carrying the disease she is now immune to, ready to start a massive pandemic, fully sponsored by the government. And condoned by Captain Kirk, no less. Let's hope they keep control of it while they still have it...
* InnerMonologue: Instead of the usual CaptainsLog, we hear Kirk's reverberating thoughts about what may have happened to his crew. And why does his arm hurt?
* LiteraryAllusionTitle: A mix of two Biblical myths. Cain killed his brother, reducing the known world population to three and was forever marked for it. Gideon used arbitrary methods to reduce the size of his army.
* MakeanExampleOfThem: Partly inverted, since the message isnít about punishment, but about salvation.
-->'''Hodin:''' No, her death at so young an age will let the people know for certain that our lifecycle can be changed. It's the symbol that'll bring forth [[HeroicSacrifice the dedicated young volunteers]]. [[RestartTheWorld The serum in their new blood will change Gideon, and it will once more be the paradise it was.]]
* ObstructiveBureaucrat: Admiral Fitzerald, the rest of Starfleet Command and the Federationís Bureau of Planetary Treaties.
* MetaphoricallyTrue: The Gideons never said their planet was a Paradise. They just said the atmosphere was pristine and no one was ever sick. That's what's making the place unbearable.
* NightmareFuel: First, Kirk must cope with the AdultFear that the people he is responsible seem to have disappeared without a trace. And then those mysterious green faces out in space accompanied by a creepy ScareChord. So many of them scraping up against the hull of the ''Enterprise'', and in the vacuum of space no less! Captain Kirk hasn't had this many people rush a vehicle he was in since Shatner drove to Comic Con!
* OntologicalMystery: Kirk beamed from his ship...to his ship...or is it his ship?
* OutOfCharacterMoment: Perhaps George F. Slavin and Stanley Adams didnít need to know TheKirk himself survived to a [[Recap/StarTrekS1E13TheConscienceOfTheKing similar massacre]], but they should have known [[TakeAThirdOption he doesnít so easily accept no-win scenarios]].
* PlanetOfHats: Kirk is kidnapped by a race whose universal pro-life tendencies had lead to horrible overpopulation, to the point that they tried to start a pandemic with germs from Kirk (who had been exposed to meningitis in the past). Kirk flaunts Humanity's "freedom" hat by stating categorically that he does not want to stay on this planet as their own hemlock dispenser and instead suggests using one of many forms of birth control the Federation had to offer. (Um...you remembered to use one on Odona, right, Kirk?)
* PlotHole: [[WorfHadTheFlu Did the computer have a throat infection this week?]] Trying to consult its databanks and the record tapes as usual would have been more useful than looking at windows.
* PopulationControl: the planet's failure to deal with this led to ridiculously extreme overcrowding (though no problems with health or resources, apparently).
* PrinciplesZealot: People of Gideons are against contraception because love and life is sacred, so bringin death and sickness is the only acceptable solution.
* RecycledSet: Apparently a world that is overpopulated with wall-to-wall people has the space and resources to build an entire fake Enterprise just to get Kirk's blood.
* RidiculouslyLongPhoneNumber: Are the proper co-ordinates 875020709 or 875020079?
* SendInTheSearchTeam: Spock wants to do this to find Kirk, but [[ObstructiveBureaucrat neither Gideon or the Federation]] will give permission to do so. He decides ScrewTheRulesImDoingWhatsRight and beams down to go InSearchOf Captain Kirk himself.
* TemptingFate: When Spock decides he will look for Kirk by himself (asking another crew member to accompany him would just get him in further trouble with Starfleet) he announces "I will not be long." Scotty points out that Kirk said the same thing. Wonder if he's seen ''Film/{{Scream 1996}}?
* WellIntentionedExtremist : Gideons are ready to use [[UtopiaJustifiestheMeans lethal and painful methods to restore their paradise]].
* WeWillHaveEuthanasiaInTheFuture: An extremely overpopulated world is trying to set up a voluntary suicide system, starting by infecting the leader's daughter with a disease.
** You'd think they find a better way to euthanize people than some painful, (relatively) drawn out disease. Maybe they're all masochists? Odona certainly seems to have a fascination for pain...
* [[WhatIsThisThingYouCallLove What Is This Thing You Call Pain?]]: Odona is morbidly curious about pain and sickness, having never felt it before.
* WouldBeRudeToSayGenocide: Self inflicted genocide, no less. Because of the horrible overpopulation and that horrible healthyness, you see. But no birth control, because we love life so much, you know. So instead of ordering us some starships, we would much prefer your painful disease now.
* TheXOfY: The Mark Of Gideon