We start with "space mission" chatter running all through the opening credits ("Somebody better start melting pretty soon or I'm going to lose interest."), and then it's on to a pretty good Apollo command module interior (I can wonder if they got passed on from production to production) with astronauts in less successful spacesuits or something. ("Now can you stir the tanks without killing us this time?") One moustached astronaut says in a somehow peculiar way that there's nothing like seeing the sun through the rings of Saturn (also managing to talk to mission control in real time), and then, for all that the stock footage doesn't seem to allow for the rings of Saturn, it does allow for a solar flare. Astronaut Steve West sort of freaks out and gets a nosebleed, the blood obligingly running down his face despite his (apparently) being in free-fall.
It's on to a hospital on Earth, where the other two astronauts have vanished but Steve West is in a hospital bed and encased in bandages, watched over by a full-figured nurse in a tight outfit and a doctor. The doctor who happens to be black tells the nurse to get some whole blood this time for another transfusion, but to still keep things under wraps, which manages to leave Steve alone. He rouses, effortlessly breaks through the straps, and sees his hands aren't in the best of shape... ("I've been jerked!") Ripping off the bandages reveals that, in the words of the official episode guide itself, "Man has begun to Melt, though not yet Incredibly." ("Aah! I'm a dried applehead!") Steve starts to trash the room, but when the nurse returns with the blood he goes after her instead. The nurse flees at length, smashing straight through a glass door instead of bothering to open it, but Steve catches up...
The doctor and another doctor ("Dr. Mod and Dr. Groovy."), Dr. Ted Nelson, find the chewed-away nurse and discuss the case; a general tells Ted Nelson to find Steve before seven the next morning. In the meantime, Steve, still in his pyjamas, has melted in no time at all into a slime-covered skull; he rips the head off a fisherman ("Hey, you got protoplasm in my peanut butter!") and then doesn't kill but probably utterly traumatizes a young girl ("Hey, no screaming unless melting men are after you!") Ted Nelson discusses the case with his pregnant wife and tries to track down Steve's radioactive trail with a geiger counter ("Maybe if we're lucky, he'll get gored by a radioactive elk."), then tries to explain away the fisherman's death for a local sheriff; Steve is constantly flashing back to the space mission chatter as night falls. ("It's mellow countdowns of the 70s.")
In a sudden tonal shift towards goofiness ("Someone switch reels on us?"), the mother of Ted Nelson's wife and her new boyfriend try to make up for being late for dinner by raiding a lemon grove; things get back on track when Steve finds them... He then, in what might be an attempt at pathos, shelters in a graveyard. ("Those old folks gave him a taste for aged meat." "God bless Runny, and Drippy, and Sticky...") The general has stopped over at Ted Nelson's house and chews him out for discussing the case with his wife, then sticks around to eat leftover turkey as Steve lurks outside. ("Well, I suppose I could reminisce about my countdown again; that could kill some time.") Ted Nelson drugs his pregnant wife so she can sleep and winds up letting the sheriff in on the secret; the general doesn't have the chance to find out before Steve kills him.
Steve then menaces a somehow "rural" young woman, killing her boyfriend or whatever; despite freaking out she manages to barricade herself in her kitchen and chops off one of his arms with a butcher knife; the camera then lingers on her huddled in the corner. ("Give her a wire monkey and see how she reacts!") Invigorated all the same, Steve heads for an industrial complex of some sort ("He's gonna meet up with the Indestructible Man!") as Ted Nelson and the sheriff close in for the protracted conclusion. At last, the two have Steve cornered on a gantry; despite Ted Nelson's apparent efforts to protest ("Maybe there's a rider in his contract that he'd be in the movie but he wouldn't have to emote."), the sheriff shoots Steve twice in the chest with a shotgun. Steve just tosses him over the edge and into some powerlines, producing a fireworks display in its own way incredible. Ted Nelson falls over the side and, just hanging on, keeps screaming his name another things at Steve; apparently this finally gets to him and he helps him up again. ("Okay. When you grab my wrist a lot of me is going to slide off, so be careful.") Two security guards have closed in, and Ted Nelson screams his name at them too, but it doesn't work as well with them as they shoot him and then Steve. He proves somewhat harder to kill...
At a low ebb at last, Steve makes it back down to the ground, collapses against a building, and melts completely down. ("You know, he may not recover from this.") Morning dawns with lingering glimpses of the scattered corpses. ("What could there possibly be to wrap up? Everybody's dead!") A janitor finds the bloody offcuts left of Steve and starts cleaning up ("So, how many monster movies end with a janitor scooping the monster into a garbage can?") as a radio reveals that another space mission is about to be launched at seven in the morning, not helped by study of the melting case... However, in one last touch of sloppiness, the first bit of stock footage is of a Saturn IB rocket with an Apollo spacecraft on top, and the second bit of footage is of a Saturn IB rocket without an Apollo spacecraft on top... ("Cape Kennedy was renamed Cape Ted Nelson, then quickly renamed Cape Kennedy again.") Although the people in the movie have apparently learned nothing in that specially bleak 1970s fashion, our heroes do discuss what they learned over the end credits.
The "host segments" deal with Crow trying to make a movie of his "Earth versus Soup" screenplay, which he wrote several seasons back; it's an admitted attempt by the Best Brains to work through their issues about studio interference with "Mystery Science Theater 3000: The Movie" with Dr. Forrester chugging water from increasingly larger bottles and his mother taking a particularly evil turn as the other studio executive. There is some poking fun at "Crow the director" too, though. In the brief and perhaps already pre-elegaic preview of the seventh season in the official episode guide book, there's a comment that "The Incredible Melting Man" might "nose out" the legendary "Manos: The Hands of Fate" as the worst movie ever on the show; that doesn't seem the case to me, but the experience is memorable all the same.