While on route to the planet Arianus on a mission to decontaminate its polluted atmosphere, the Enterprise intercepts a Federation shuttle that had been reported stolen from Starbase 4. After disabling the shuttle, its alien pilot is brought on board: though humanoid, said pilot's skin is half ink black, half chalk white, right down the middle. Spock is extremely intrigued, claiming said coloration goes against all genetic theory and that the pilot might be one of a kind.
The captive pilot wakes up and introduces himself as Lokai (Lou Antonio), from the distant non-Federation planet Cheron. However, when asked as to why he stole the shuttle, he becomes evasive and refuses to explain further. After contacting Starbase 4 and informing them they will return the shuttle as soon as the Arianus mission is complete, the Enterprise is suddenly approached by an invisible alien ship on collision course. However instead of colliding, it disintegrates and its pilot suddenly appears on the bridge. Said pilot is apparently the same species as Lokai, having the exact same skin colors only reversed (so much for "one of a kind"). The alien introduces himself as Bele (Frank Gorshin), also from Cheron and Chief Officer of its Commission on Political Traitors. Bele claims Lokai is a fugitive convicted of treason and he has been sent to apprehend him.
The two aliens meet and get into a heated argument, with Lokai claiming Bele's race has enslaved Lokai's and planning on their genocide while Bele claims Lokai's people were "savages" that were "educated" by his own people, and that Lokai has caused his race to engage in violent revolution resulting in the deaths of thousands. Lokai asks Kirk for political asylum while Bele demands that Lokai be handed over to his custody. Kirk refuses to take sides claiming that Lokai is a prisoner of Starfleet (and thus ineligible for asylum) over the shuttle's theft and since Cheron is not a Federation planet Lokai cannot be extradited there. He adds that as soon as the Arianus mission is complete, they will have to make their case at Starbase 4. Bele is displeased at this and uses some mysterious power to take control of the ship, claiming he has been chasing Lokai for "fifty thousand of your terrestrial years" and he won't give up now.
After phasers prove to be useless, Kirk threatens to set off the Self-Destruct Mechanism if he doesn't return command of the ship. Bele thinks Kirk is bluffing to which Kirk responds by ordering the verification of the self destruct sequence by the vocal commands of himself, Spock and Scotty. Only a few seconds away from the end of the countdown does Bele release control. He adds that he will allow the Arianus mission to be completed and requests that he be allowed to bring Lokai to Cheron as soon as it's done. Kirk makes no promises but allows both to walk freely within the ship.
En route to Arianus, Lokai makes his case with the crew, claiming humans have no idea what it's like to be persecuted, and not being impressed when he is informed that persecution did occur in the distant past of human history but mankind has evolved past it. Meanwhile Bele is relayed a message from Starfleet command claiming that Lokai will stand trial on Starbase 4 and that it's likely that he will end up turned over to Bele's custody. Bele doesn't believe it, claiming Lokai will manage to manipulate everyone into releasing him and calling him "an inferior breed". When Spock calls him of the same breed as Bele, Bele points out the difference that Lokai and his "people" are white on the right side while Bele's race is white on the left. Spock's claims that Cheron's people can overcome such differences just like Vulcan once did are interrupted by the Enterprise arriving at Arianus.
The decontamination procedure goes without problems. However, as soon as the course is changed to Starbase 4, Bele hijacks the ship again, this time making sure to burn out the self destruct controls, leaving Kirk and the crew no choice but stand around helplessly while the ship is taken to Cheron. Lokai appears on the bridge outraged at this development and fights Bele, threatening to tear the ship apart though Kirk calms them down. Kirk is given control back once Cheron is in visual range. However, the surface scans pick up a grim sight: completely empty cities filled with unburied bodies, animals and vegetation encroaching on them. Every sapient life form on Cheron is dead, having wiped each other out in a giant race war. The shocked Lokai and Bele promptly turn on each other again, accusing the other's race of being responsible. Kirk pleads with them to stop fighting, claiming that their hatreds are pointless now and that they're welcome to live in the Federation. Kirk's pleas fall on deaf ears and Lokai and Bele take the fight down to the destroyed planet, leaving the crew to ponder on the pointlessness of it all:
Tropes featured in this episode:
- Artistic License Biology: Spock claims that the evolution of bichromatic skin colour is highly unlikely. One look around the animal kingdom learns that this is blatantly untrue, as any zebra, clownfish or parrot will tell you.
- He mentions that there would be no purpose for such a dichromatic division to be right down the center, though.
- The closest to exact Cheron coloration in zoology would be Chimera cats like Venus here. Of course, this is a rare case of two zygotes (each with a distinct genome) fusing and developing into a single organism.
- "Ass" in Ambassador: Bele does a poor job of representing his people with civility.
- Bottle Episode: Another one that only takes place on the Enterprise.
- Coconut Superpowers: No budget for a spaceship model? No problem... it's invisible.
- Creepy Monotone: Scotty, when reciting his codes to activate the self destruct sequence.
- Determinator: Bele says he has been pursuing Lokai for 50,000 years and not even the destruction of life on their planet stops him.
- Doomed Homeworld: Cheron.
- Downer Ending: A whole race gets wiped out, to the last man, and for once there's not a single thing the Enterprise crew can do about it. They are forced to let the last two survivors chase each other down to the planet to continue the senseless conflict for its own sake.
- Everything Sensor: The ship's sensor can detect anything on Cheron down to corpses lying in the street. Makes you wonder why they need an away team most of the other times they visit a planet for research...
- Fantastic Racism: Not only do Bele's and Lokai's people have this for each other, but Bele seems to have a low opinion of mono-colors like our heroes.
- Grudging "Thank You": Lokai takes a break from yelling at Kirk to thank him for the rescue — and goes right back to arguing.
- Half-Breed Discrimination: Somewhat literally.
- Ham-to-Ham Combat: Every time Lokai and Bele share the screen. Kirk makes it a verbal Mêlée à Trois.
- Implacable Man: A 50,000 year lifespan and the ability to take control of a starship through willpower put Bele in this category.
- Inspector Javert: Bele's pursuit of Lokai is obsessive enough to make him an example of this trope, but we don't know how justified his accusations against him were.
- Invisibility Cloak: Bele's ship is sheathed in materials that make it invisible, although it still shows up on sensors.
- Jitter Cam: Every time a red alert sounds in this episode, the camera repeatedly zooms in and out at the flashing light. This was a Shout-Out to the Batman TV series, as Frank Gorshin (the Riddler) plays Bele.
- Kirk Summation: At the end of the episode, the good captain attempts to sermonize Bele and Lokai about the futility of their battle; pointing out that their entire planet, Cheron, as well as all of the entire rest of their people, have been completely and utterly devastated during their absence as a result of the bickering between the various groups... surely the two Cherons can find a common ground in the wake of this catastrophic event.
- Let Me at Him!: Both ways between our two guests.
- When they first meet face-to-face at sickbay, Lokai sits there smoldering at Bele until he smugly mentions how he sees how "quiescent" he is; at this, he starts up from the bed and Kirk restrains him...
- ...and at the other end of their back and forth, Bele, increasingly nettled, gets himself into it at "You're coming back with me to pay for your CRIMES!!!" and goes for him.
- Obstructive Bureaucrat: For once, Kirk gets to play this, insisting that both aliens go through the Federation first, and firmly staying out of foreign politics.
- Plot Hole: If Cheron is in uncharted space, how does Kirk know about it, and how can Sulu determine the ship is plotting a course towards it?
- Kirk mentions that Cheron is generically located in the "southernmost" (on the up-down axis, as opposed to those in the same plane as the galactic arms) part of the galaxy. Presumably any deviation from Starbase 4 in that direction, especially given the ludicrous speeds the Cheron natives can accelerate the Enterprise to, would be obvious.
- Profiling: Bele is guilty of this during his famous "All of his people are white down the RIGHT side" speech.
- Really 700 Years Old: The aliens from Cheron have been chasing each other around the galaxy for 50,000 years.
- Scifi Writers Have No Sense Of Scale:
- Bele claims to have been chasing Lokai for fifty thousand years, which is utterly gratuitous and raises a lot of questions that never get answered; there's no reason it couldn't have been, say, fifty years.note
- The second time Bele commandeers the Enterprise to get to his distant home planet, the trip is way too short; by the time our heroes have finished discussing the fact that the ship has been commandeered, they're there. Bele needn't have taken the trouble to disable the self-destruct mechanism; there wouldn't have been time to enter the activation codes anyway.
- Self-Destruct Mechanism: The Enterprise has one which requires three ship's officers to recite activation codes to the computer.
- Servant Race: Lokai's "people" are said to have been this.
- Shut Up, Kirk!: Both of the aliens ignore Kirk's appeal, choosing to beam down to their dead planet and finish each other instead.
- Silly Reason for War: How pretty much everyone on the Enterprise views a war being fought because one side is white on the left side and black on the right, while the other side has it the other way.
- Stealth Pun: Cheron is in the southernmost part of the galaxy, in other words, the Deep South.
- Stock Footage:
- The close-up of Chekov's hand operating the decontamination of Ariannus is a recycled shot of Kirk's hand from "The Doomsday Machine". (It was also used as Spock's hand in both "Obsession" and "The Immunity Syndrome".)
- The final chase scene depicting Lokai and Bele running through the corridors of the Enterprise is mixed with stock footage of burning cities filmed after WW II aerial bombing raids, as each visualizes the destruction of their shared home planet. Fred Freiberger stated, "We ran a little short on that show which is why it ended with a chase that went on forever. I thought it was a hell of a creative solution."
- Sufficiently Advanced Aliens: Bele flies an invisible spaceship, can commandeer the Enterprise without physically interfacing with the ship, and (along with Lokai) has a lifespan in the tens of thousands of years, if not more.
- Taking You with Me:
- When Bele will not release control of the Enterprise, Kirk activates the ship's self-destruct sequence and tells him that while Bele may control the Enterprise, the final order is Kirk's.
- Bele and Lokai then try to do this with each other.
- Title Drop: Not word-for-word, but at one point during Bele and Lokai's struggle on the bridge, Kirk does reference the Enterprise being "your last battlefield". Ironically, and tragically, it seems this will be true of their planet which was already devastated by their races' last battle.
- Tractor Beam: Used to bring Lokai's stolen shuttle aboard the Enterprise.
- Two of Your Earth Minutes: When Bele makes the claim that he's been chasing Lokai for 50,000 years, he specifies that he's speaking of "your Terrestrial years".
- White Man's Burden: Bele tries to invoke this.
- You Are What You Hate: Bele does not respond favourably to Spock's theory that his "people" and Lokai's "people" evolved from a common ancestor.
- You Can't Go Home Again: Averted, both aliens return to the destroyed Cheron, presumably to finish their fight once and for all.