'''WARNING:''' This episode contains rapidly flashing lights, colors and disorienting imagery that may trigger epileptic seizures in photosensitive persons. Reduce the risk by viewing in a well lit room.

OK, boring warnings out of the way, onto the plot! The ''Enterprise'' is hosting a visit from the Medusan ambassador Kolos and his companion Dr. Jones. Spock is given the duty of beaming aboard the ambassador as only his Vulcan sensibilities combined with a special visor can prevent him from going mad at the sight of a Medusan. Dr. Miranda Jones, however, is quite easy on the eyes. You can tell how captivating her beauty is in that Spock slightly raises a brow on his otherwise impassive face.

A formal dinner is held. Unfortunately, due to the fact that he is an EnergyBeing and one whose sight causes madness in humans, Kolos cannot attend. It's revealed that Dr. Jones is a born telepath- rare among humans. She has lived on Vulcan to better learn control of her abilities. She excuses herself, saying that someone on the ship is contemplating murder. When an engineering genius called Marvick follows, she realizes it's him. Marvick desires Dr. Jones, who is in love with Kolos. Marvick may have designed the engines of the ''Enterprise'', but he can't figure out why she'd choose someone charming, intelligent, insightful and congenial over a selfish, sexist, hateful and brash whiner like him.

Marvick decides he'll MurderTheHypotenuse of this LoveTriangle. Yeah, just sneak up and pull a phaser on that mini-EldritchAbomination. [[WhatAnIdiot Great idea.]] Next thing we know, Marvick has strangled a RedShirt, KO'ed several others, taken control of the ship and drove into an alternate universe filled with nothing but purple clouds as far as the eye can see. And then he's inconsiderate enough to die before steering them out! But wait, Kolos is a navigational expert! All he needs is a physical body. Dr. Jones volunteers, but there's just one problem. [[SorryBillyButYouJustDontHaveLegs She's blind and]] [[Series/StarTrekTheNextGeneration the VISOR]] hasn't been invented yet!
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Looks like it's up to you, Spock!
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Tropes from this episode include:

* AcePilot: Kolos is an incredibly good pilot, capable of driving a starship through a NegativeSpaceWedgie with an unmatched precision.
* BlindSeer: Dr. Jones is a blind telepath
* BrownNote: Viewing a Medusan unprotected will drive most people irreversibly insane.
* ColorMotif: The color green is used often in this episode where envy is a theme.
* DisabilityImmunity: Since Dr. Jones is blind, she can't be driven insane by Kolos' appearance. Using her telepathy to communicate with him, she learns that he's really a decent guy and she [[BlindAndTheBeast falls in love with him.]]
* DontYouDarePityMe: Dr. Miranda Jones considers pity to be the worst of all the human emotions, partially because of her blindness and partially because of her attachment to Medusan ambassador Kolos, whose people are said to be so hideous, they drive any humanoid who sees them to madness.
* EldritchAbomination: A rare case of a jovial and friendly one. Just don't look at it.
* GemEncrusted: Dr. Jones wears a gem studded net shawl over her dress. It is revealed to be a high tech sensor web that helps her detect objects' distance and movement.
* GiveGeeksAChance: At last, [[TheCasanova even Kirk]] strikes out, losing to a disembodied life form whose appearance causes insanity. (Hinted to be considered a "geek" among alien races.)
* GogglesDoSomethingUnusual: The red goggles prevent people from going mad while looking at a Medusan, provided they also have extensive mental training.
* GoMadFromTheRevelation: What happens when someone looks directly at a Medusan.
* GreenEyedMonster: Marvick is envious of Jones's love for Kolos. (It can't be called jealousy as he never had her love to start with.) Dr. Jones is envious of Spock's superior mental abilities.
* IdiotBall: Marvick must be carrying one to think assassinating a mini-EldritchAbomination is a good idea. Scotty can be forgiven for endangering the ship since, after all, Marvick was one of the designers of the ''Enterprise'' engines and it wasn't like he was wearing a sign that said "Hello, I'm crazy today". The ball must've been picked up by Kolos who just forgot that his host needed those red goggles to look at himself without making his host lose his mind. Kirk suspects that Dr. Jones used her telepathy to make him forget. She denies it.
* InformedAttractiveness: The men are constantly falling all over themselves to tell Dr. Jones how beautiful she is.
* InformedUgliness: Everyone refers to Kollos as so ugly it drives people insane, but as Jones points out, it might as well be insanity-inducing beauty.
* LiteraryAllusionTitle: Straight from a George Herbert poem, ''Jordan''.
* LoveMakesYouCrazy: Marvick wasn't exactly playing with a full deck even before he was exposed to Kolos' true form.
* MeaningfulName: "Medusan" obviously is inspired by Medusa of GreekMythology. Kolos hints this is only what others call his race, not what they call themselves. Dr. Jones' first name is Miranda, meaning "Fair to look upon". She certainly is attractive. Kirk calls her "The loveliest human to grace a star ship." Kolos realizes her connection with the character from Theatre/TheTempest when he says "O brave new world that hath such people in it."
* MentalFusion: Spock Mind Melds with a Medusan to save the Enterprise.
* NegativeSpaceWedgie: When Mavrick goes crazy and takes over the ship, he ends up flying them through one and stranding them beyond the known galaxy. Spock has to merge with Kolos to fly back through it, lest the ship be forever stranded outside the galaxy.
* POVCam: We can tell Spock's crazy when his POV is shot from a FishEyeLens.
* HeyItsThatGuy: Diana Muldaur isn't really a doctor, but she's played three of them on ''Franchise/StarTrek''. Besides Dr. Jones, she's also been Dr. Ann Mulhall in "Return to Tomorrow" and in ''Series/StarTrekTheNextGeneration'' she plays Dr. Katherine Pulaski.
* RightForTheWrongReasons: The Enterprise crew argues that Dr. Jones, even if she telepathically links with navigational expert Kollos, cannot help pilot the ship back because she's blind, so Spock is chosen instead. The assertion that her blindness is an issue seems ridiculous since her sensor net allows her just as much ability as anyone with natural sight. However, the completely correct assertion that she is not qualified to be at at helm while Spock most certainly is never seems to occur to anyone.
* SufficientlyAdvancedAlien: The Medusans.
* TakeOurWordForIt: The sight of a Medusan is so hideous it drives one of the Enterprise's chief designers completely insane. The flashing lights might not drive a viewer insane, but it just might trigger epileptic seizures. They're also supposed to have the most sublime thoughts in the galaxy, but that's only applicable to a telepath.
* [[WhenSheSmiles When He Smiles]]: This is one of few episodes where Spock is seen smiling. It does wonders for his looks.
* {{Yandere}}: Marvick demands Dr. Jones loves him and goes to kill Kolos when she won't. Dr. Jones is accused of hovering on the edge of being one. It isn't proven.