Personally, I'd steer clear of all Kryptonite-colored puke nebulae, but Kirk has standing orders from Starfleet to fly inside and see whether or not it's an open bar.
The Enterprise happens to be schlepping the Galactic High Poobah to a tea-totaling plague planet called Marcus Welby III. I'm guessing by his no-nonsense attitude that he's the Dean Wormer of the Federation, and he insists that Kirk steer clear of all fun so they can make their rendezvous and deliver his load of lifesaving Fizzies on time.
I'm pretty sure the Galactic High Poobah was also the guy who played the mayor of San Francisco in a Dirty Harry movie, but not the one where the mayor really was Dean Wormer. The Galactic High Poobah was a different mayor in that Dirty Harry where the mayor gets kidnapped and winds up on Alcatraz and either Cagney or Lacey gets shot at the end. I don't know which. The fat one who was married to the black guy from The Rookies, not the other fat one who wasn't.
Kirk sends Spock out in a shuttle to investigate the Kawasaki phenomenon that makes the sky look like green beer puke. Why Spock has to go in a shuttle is never adequately explained, since it seems like it'd make more sense to take the Enterprise in there. It's not like they can't take the Enterprise in, because they do so at the end to rescue Spock whose shuttle crash lands in a minute. (Uh-oh. Just act surprised when it happens.)
Spock's shuttle crash lands!
A crash-landed shuttle is such a great, original concept to spark a story. And I'm sure it will stay that way, because this is a one-off deal and Star Trek won't flog the whole "shuttle crash lands on alien planet, hilarity ensues" concept to death over the next forty years. So enjoy this once-in-a-lifetime concept this one time, because you'll never, ever see it happen again.
Down on the alien, smog-enshrouded planet, Spock sends crewmen Larabee and Gelato out to get killed...oops, I mean to reconnoiter. He orders them to keep the shuttle in sight at all times, so naturally they wander forty miles out into a fog-filled valley then close their eyes and spin around a couple dozen times to make the trip back more excitin'.
The two crewmen stumble upon an abandoned summer camp where all those sexy teenagers died ten years ago, and naturally Larabee or Gelato (who cares which one?) gets murdered by a giant, Styrofoam-rock-heaving gorilla-man.
Spock shoots a laser beam around, and the giant gorilla-men run away. At least I think they do. There is no budget to show more than the back of a head or a shoulder or something. They do toss in some giant plastic spears, which I suppose would be pretty scary if they took the tips off because you could put out an eye. (This public service message courtesy my mother who told us not to take the rubber tips off the darts in our dart guns, even though we did it all the time anyway and none of us ever lost an eye.)
Spock says they'll die for sure with nothing to eat if they stay on the planet. Way to boost morale, Commander Bring-Down. I thought this guy was supposed to be King Logic? You've got ray guns to shoot the gorilla-men, so that takes care of them for as long as the juice in the ray guns hold out. And instead of giving up on eating so easily, maybe you could -- oh, I don't know -- find out what the giant gorilla-men are eating and drinking. 'Cause logically they must be eating something other than Styrofoam rocks and plastic spears. And those pelts they're wearing aren't mail orders from L.L. Bean, so there are potentially tasty animals out there you can hunt. Or maybe Starfleet survival training consists of waving around an EBT card and demanding free Froot Loops from every King Kong alien that walks by, followed by starving to death if they don't immediately pop open the pantry.
I think Spock must have them dig a latrine. Also, Spock is a toilet exhibitionist a la Lyndon Johnson. That's the only explanation I can come up with for why at one point they're all squatting around outside in full view of aggressive aliens who have already killed a crew member and are not hiding behind some Styrofoam rocks.
To suggest that I should courtesy flush out here is illogical. Jerks.
Upstairs, Kirk decides to bring the Enterprise in where he should have brought it before and search for the tiny little ship that wouldn't be lost if he had taken the big ship inside the puke cloud to begin with. Also Mayor Grand Galactic Poobah is hollering at him that if they don't get to planet Marcus Welby III on time, all the best geosynchronous parking spaces will be gone.
Downstairs, Spock carts dead Gelato back to the shuttle and gets big plastic spears tossed at him. He says they don't have to shoot the King Kong gorilla-men monsters, they only have to shoot above their heads and they'll be so impressed by the pretty light show that they'll applaud and wander away. Did this guy really go to Vulcan logic school, because I'm pretty sure with that stupid plan by the end of the episode Spock and everybody else on the shuttle will be roasting on a spit with space-apples stuck in their mouths.
Up on the Enterprise, a second plastic toy shuttle doesn't find Spock. Probably because it's only four inches long.
Down on the planet, the monster gorilla-men attack the crash-landed shuttle, but the budget only paid for one to be seen on camera and, like all the rest of the monster gorilla-men, you can only see little bits of him from a distance.
Inside the shuttle, Scotty flicks the porch lights a couple of times and the monster gorilla-men run away before they can set fire to the bag of dog poop.
Scotty says that if he takes all the phasers and channels their power into the flux capacitor, he can get the shuttle back to 1985.
Drama is had by an impromptu funeral for Gelato which Spock correctly says is stupid and dangerous, and also by one guy being so insubordinate to Spock that he should be tossed in Space Leavenworth for the rest of his life.
We're supposed to think that Spock is wrong to not get all weepy and risk everyone's life by having a funeral in the backyard of aggressive gorilla-man space monsters, but he seems pretty vindicated to me when the gorilla-man monsters attack during the buffet after the funeral and Spock gets his foot caught in some Styrofoam rocks near the table with the deli platters and stale Chips Ahoy.
The shuttle takes off just as the Enterprise has abandoned its search because if Kirk doesn't leave pronto the Dirty Harry mayor has threatened to show him naked pictures of Officer Cagney or Lacey.
Kirk drives away very slowly like an old lady but, unlike the old lady who backed into my parked car in the parking lot that time when I was taking a nap during my lunch break at work years ago, at least he keeps checking the rearview mirror.
Spock dumps all the fuel out of the shuttle and sets fire to it to act as a big road flare, which means that the shuttle is going to burn up in the atmosphere and everyone is going to die. He thinks it's hopeless and that the Enterprise won't see the gas burning. If it was so hopeless, maybe it would have made more sense once they got the shuttle flying again to find an island or somewhere on the planet where the gorilla-men aren't living and set up a permanent camp there. Or, you know, sentencing everybody on the shuttle to a fiery death is a pretty good command decision too.
Spock's makeshift flare is seen from the Enterprise, the plastic toy shuttle is brought aboard, and everybody is happy except Gelato and the other guy Spock's crummy leadership allowed to die down there. Also the guys from the search party who died as well. But they weren't main characters, so it's okay.
Kirk says Spock panicked when he set fire to the gas, and Spock says that panicking was the logical thing to do, and everybody on the bridge starts laughing so maniacally I'm pretty sure Bones must be venting nitrous oxide through the air vents.