'''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.

[[caption-width-right:350:Spock and his sweet-ass visor.]]
OK, boring warnings out of the way, onto the plot! The ''Enterprise'' is hosting a visit from the Medusan ambassador Kollos 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, Kollos cannot attend. However, Dr. Jones does attend, as does Dr. Larry Marvick, an engineering genius who has been working with Kollos and Dr. Jones on a project to combine Medusan navigation know-how with Federation starship technology. 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. Marvick also excuses himself, and follows her back to her quarters. Marvick desires Dr. Jones, and has repeatedly refused to accept that she's not interested in him, and certainly not willing to entertain his demand that she give up her career among the Medusans so they can be together. She tells him to get lost, and very kindly doesn't have him arrested for harrassment.

Marvick decides the only sensible thing to do is [[MurderTheHypotenuse put Dr. Jones out of a job by murdering Kollos]]. Yeah, just sneak up and pull a phaser on that mini-EldritchAbomination. [[WhatAnIdiot Great idea.]] Next thing we know, Marvick has strangled a RedShirt (Scotty. He gets better), KO'ed several others, taken control of the ship and driven 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, Kollos is a navigational expert! All he needs is a physical body. Dr. Jones volunteers, but there's just one problem. [[DreamCrushingHandicap She's blind and]] [[Series/StarTrekTheNextGeneration the VISOR]] hasn't been invented yet!

Looks like it's up to you, Spock!
!!Tropes from this episode include:

* AcePilot: Kollos 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.
* DeathByDespair: Apparently, this is the cause of Marvick's death. In his madness, he sees Miranda as some murderous being, and he can't reconcile it with his love for her. So, he just dies.
* DefrostingIceQueen: Dr. Jones is very frosty, warming up at the very end.
* DisabilityImmunity: Since Dr. Jones is blind, she can't be driven insane by Kollos' appearance.
* 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 Kollos, 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.
* 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 attachment to Kollos. (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 Kollos who just forgot that his host needed those red goggles to look at himself without making his host lose his mind. Spock seems to have caught it too. Kirk suspects that Dr. Jones used her telepathy to make him forget. She denies it, but her jealousy makes it a very real possibility nonetheless.
* InformedAttractiveness: The men are constantly falling all over themselves to tell Dr. Jones how beautiful she is.
* InformedDeformity: Everyone refers to Medusans as so ugly it drives people insane, but as Jones points out, it might as well be insanity-inducing beauty.
* LeftYourLifesaverBehind: Spock forgets the visor which would protect him from Kollos' appearance when he goes to undo the mind link. It's hinted that Dr. Jones ''may'' have been the cause behind this, but isn't confirmed.
* LiteraryAllusionTitle: Straight from a George Herbert poem, ''Jordan''.
* LoveMakesYouCrazy: Marvick wasn't exactly playing with a full deck even before he was exposed to Kollos' true form.
* MeaningfulName:
** "Medusan" obviously is inspired by Medusa of Myth/GreekMythology. Kollos hints this is only what others call his race, not what they call themselves. (According to Shane Johnson's ''The Worlds of the Federation'', which is semi-canonical, their planet is called Visalayan and it's something like Venus.)
** 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." Kollos 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 Marvick 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 Kollos 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.
* ProductPlacement: In real life, [[http://fanlore.org/wiki/IDIC_%28Star_Trek_term%29 the Vulcan IDIC]] was created as a way for Gene Roddenberry [[http://startrekfactcheck.blogspot.com/2013/08/dont-know-much-about-vulcan-philosophy.html to sell merchandise]]. After protest from the actors, its presence was trimmed down considerably.
* TheReasonYouSuckSpeech: Kirk is near-heartbroken at the prospect of losing Spock and channels that into pure rage as he tells Dr. Jones what he thinks of what he perceives as half-hearted attempts to revive Spock.
--> [[LampshadeHanging "With my words, I'll make you hear such ugliness as Spock saw when he looked at Kollos with his naked eyes!"]]
* 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's not qualified to be at at helm while Spock most certainly is never seems to occur to anyone.
** However, it's only said that the sensor web allows Miranda to judge distances and recognize objects in general. Nothing is said about it allowing her to read the gauges on the control panels or watch the viewscreen. Without that ability, piloting a starship under those conditions would be at best unadvisable, and at worst impossible.
* ShipTease: While mentally merged with Kollos, Spock quotes love poetry to Uhura.
* ShoutOut: Kollos-Spock quotes Byron ("She walks in beauty like the night") and Shakespeare ("O brave new world, that has such people in it!")
* 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, another reason they need a telepathic counterpart who can interpret.
* WhamLine: In-Universe. When Miranda states she'd be better at melding with Kollos than Spock, [=McCoy=] objects, saying that while she can do many things, piloting a starship isn't one of them because it requires ''sight''. Kirk and Spock are visibly taken aback at this.
* [[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 Kollos when she won't. Dr. Jones is accused of hovering on the edge of being one. It isn't proven either way.