The episode starts off as most episodes start off: with the Enterprise on its way to a planet for Kirk to screw around with. Only this time... there's no planet. The entire system they were assigned to go to has been wiped out of all organic life forms, leading the crew to wonder just what the hell is going on. The answer comes in the form of a tiny pod firing massive amounts of photon fire at the ship, resulting an a weak retaliation and the most ludicrous exchanges known to mankind:
Kirk: Fire photon torpedoes.
(torpedoes are launched, they do nothing)
Spock: No effect, the probe that fired the blast absorbed the torpedo.
Kirk: [incredulous] How can that be? Nothing can withstand a photon torpedo blast.
Anyway, Kirk orders a hail to the probe, which inexplicably stops its attacks. After some exchanges of Translator Microbes, the probe, called "Nomad", ceases hostilities, referring to Kirk as "The Creator" in the process. It's brought aboard, against the concerns of Scotty, and is let loose on the ship. This can't possibly go wrong, can it? I mean, it's not possibly like it's capable of or willing to Kill All Humans and — oh, wait, it's shown to have the power to annihilate an entire planet's worth of organics, and tells the crew that its mission is to "sterilize all imperfect biological organisms". Right then, moving on
The big three converge over what exactly Nomad is and what it's doing; it seems like the probe wasn't, in fact, able or willing to cause The End of the World as We Know It, in the first place, and its creator — Jackson Roykirk — programmed it for simple deep space exploration. By its own admission, Nomad clearly had an incident with what it calls "The Other", which altered its structure and programming, causing it to become Bender's non-alcoholic and more abusive ancestor and mistaking Kirk for its builder. Unfortunately, by the time they realize this, Nomad has already been lured to the bridge by the siren's song of Uhura, which confuses it and causes it to wipe her memory when it can't discern the logic of "music". And it kills Scotty, too, when he tries to interfere, but the machine fixes him right up afterwards, so it's no big deal. Of course, with Uhura's brain now wiped, we get a hilarious re-education subplot involving her trying to read "The dog has a ball".note
With time running out, and information on what happened to Nomad still scanty, Spock somehow manages to mind-meld with the thing (never mind that it's a robot), which causes two things to happen: Spock to talk like the robot McCoy keeps insisting he really is, and Nomad finding out that Kirk is a biological being and is, therefore, imperfect and a target for its eradication protocol. In an implausible bit of Techno Babble, it turns out "The Other" is a probe called "Tan-Ru", sent by an alien society to collect and sterilize soil samples as a prelude to colonization, and they combined during a self-repair attempt into the current Nomad. How that gave it the ability to nuke a world is left to the imagination, and there is no time to speculate, as Nomad has shut down the life support systems of the ship, threatening everyone on board. After confronting the killer probe and confirming that its death orders have no loophole, Kirk does what he does best: confuse a computer to death, by dropping the Logic Bomb that Nomad isn't perfect as it mistook him for its long-dead creator. This melts down two computers — Nomad itself, and Spock's brain, as Kirk was never one for flawless logic, but luckily they're able to beam the probe off the ship before it blows itself up.
The Fan Nickname for this episode is "The One with... Nomad". The story for this episode was the basis for that of Star Trek: The Motion Picture, resulting in one of that film's (many) derogatory nicknames being Where Nomad Has Gone Before.
Tropes for this episode include:
- A.I. Is a Crapshoot: And sometimes you get snake eyes.
- Back from the Dead: Scotty.
- Blatant Lies: Spock tells Nomad Kirk was just testing his memory banks. Odd, since Spock almost never lies.
- Continuity Nod: The song Uhura sings is "Beyond Antares", which she'd sung in full back in "The Conscience Of The King".
- Cooldown Hug: Kirk gives Spock one after a Mind Meld goes bad.
- Death Is Cheap: Scotty is killed by Nomad, then revived by it in a matter of minutes no worse for wear.
- Easy Amnesia: Nomad claims he's completely erased Uhura's mind, yet she is nearly "reeducated" by the end of the episode.
- I'm Standing Right Here: Bones is clearly offended when Nomad says that he "functions erratically."
- "It" Is Dehumanizing: Nomad refers to everyone, human or Vulcan, as a "unit".
- It Runs on Nonsensoleum: How Nomad is powered.
- Jewish Mother: Invoked by Kirk, with tongue firmly in cheek, mock-mourning the probe that thought Kirk had created it: "You saw what it did to Scotty. What a doctor it would have made. [beat] My son, the doctor."
- Just Testing You: After Kirk asks Nomad why Nomad refers to him as 'The Creator', Spock quickly interrupts, telling Nomad that 'The Creator was just testing your memory banks'.
- Kill 'Em All: Nomad's "Prime Function".Nomad: My function is to probe for biological infestation. To destroy that which is not perfect.
- Little "No":Spock: My congratulations, Captain. A dazzling display of logic.
Kirk: You didn't think I had it in me, did you, Spock?
Spock: No, sir.
- Logic Bomb:
- In the climax, Kirk convinces Nomad that it is itself imperfect by revealing that its creator, Jackson Roykirk, is dead and that Nomad mistook Kirk for him. Then he says that Nomad made another error by not discovering the first error, and then committed a third error by not sterilizing itself after the first two. This sends Nomad into a Villainous Breakdown that leads to its self-destruction.
- Also subverted earlier in the episode. Nomad came see that Kirk (who it still thought was its creator) also qualified as an "imperfect" being. When Kirk asked it how an imperfect being could have created a perfect machine, Nomad simply concluded that it had no idea.
- Madness Mantra:
- Spock says "Sterilize" over and over again after a mind meld gone wrong with the probe NOMAD.
- Nomad, after Kirk gives it a Logic Bomb, causing the probe to repeatedly shout "Error!" in a progressively higher and more distorted tone until it self-destructs.
- Mistaken Identity: Nomad thinks Kirk is his creator, Dr. Jackson Roykirk.
- Name's the Same: Played with. Nomad mistakes James T. Kirk for Jackson Roykirk.
- Only Mostly Dead: Scotty, but he gets better.
- Only Sane Man: Scotty is the only crew member who objects to bringing a planet-sterilizing superweapon aboard the ship.
- Plot Armor:
- Scotty is zapped by Nomad but revived, whereas every other Red Shirt it attacks is completely vaporized.
- Nurse Chapel somehow survives trying to stop Nomad from accessing Kirk's medical records as well, being only stunned. It happened off screen, so we don't know exactly how threatening she was to Nomad.
- P.O.V. Cam: We get a couple of them from Nomad. Once when he follows a leery Bones to sickbay, and once when he walks off with some disgruntled guards.
- Reaction Shot: When Kirk drops the Logic Bomb, the camera briefly cuts to Nomad; it doesn't visibly react, but one can easily imagine that it's thinking "WTF?"
- Red Shirt: One of the highest body counts in the series, as Nomad vaporizes at least six security guards when he breaks confinement.
- Robo Speak: This is how Nomad talks.
- Snap Back: Uhura is back to normal by the next episode, despite last being seen being taught to read again and only being able to speak Swahili.
- An earlier draft of the script had Nomad explaining it had not purged her brain completely — her memories and experiences were intact, but her ability to express language was wiped. This line was probably cut for time. They probably taught her Swahili first because it was her original language. (By the way, she first says Sikumbuka — "I can't remember" — then ina mbwa ni tufe, "the dog has a ball.") The James Blish novelization still has this version.
- Speaks in Binary: Nomad while in space. It later changes to a mathematical message requesting language equivalence.
- Title Drop: When Kirk discusses with Spock the old notion of a changeling—a creature left in place of a baby by the Fair Folk.
- Too Dumb to Live: You would think that after the deaths of the first couple Redshirts, the others would quit firing on the damn thing. But they don't.
- Touched by Vorlons: Nomad's destructive abilities were enhanced after the impact with an alien probe.
- Unexplained Recovery: Scott was tempting fate, wearing that red shirt in every episode. He got better, but six other Redshirts weren't so lucky.
- Villainous BSoD: Kirk's Logic Bomb to Nomad leaves the probe shaking and erratically shouting "Error", "Analyze", "Must sterilize" and variations thereof in a rising and distorted voice, as it builds up to self-destruct.
- Weapon of Mass Destruction: Nomad counts as one, after its fusion with Tan-Ru.
- What Measure Is a Non-Human?: Inverted. Nomad wants to kill anything that's too human. Spock is spared because he is so much more orderly than the other humans. Spock seems almost flattered to be described as such.
- Woobie, Destroyer of Worlds: Aw, he's just a little lost robot doing what he thinks he was programmed to do!
- Writers Cannot Do Math: The range to Nomad when it is firing at the Enterprise is given as 90,000 km, and the plasma bolts are travelling at Warp 15. They shouldn't be taking several seconds to impact, they should be covering that distance in a tiny fraction of a second.