serizawa3000

Thinking about what I refer to as the "This Island Earth Plot". I call it that because it seems to me the best example and I know the movie by heart. (I could also call it the "Explorers Plot" or maybe even the "Tomorrowland Plot" but like I said, I'm most familiar with This Island Earth.)
The plot in question is really yet another variation on the Hero's Journey, where there's a Call to Adventure, Mentors, Enemies, and Allies to be encountered, Trials and Tribulations to be faced, and in the end some kind of goal is achieved, but at great cost and... no small amount of disappointment due to circumstances (and short running time for the film).
Bear in mind I am about to reveal spoilers for a decades-old science fiction movie with a square-jawed hero, an adventure in space, and an all but inexplicable rubber-suit monster.
It starts out with an intriguing multi-part Call to Adventure: Scientist Cal Meacham's personal jet is about to crash when it's suddenly enveloped in a strange green light and is safely landed. Once he's back on the ground, Meacham receives a mail-order catalog from which he orders an interocitor (whatever that is. Like an Atomic Age Sampo, I guess). The machine is assembled and activated, introducing Meacham to the mysterious Exeter, who with his shock of white hair could be a Mentor figure. Exeter is looking for scientists like Meacham to assist in some kind of Great Work. Meacham jumps at the call, and is flown out (in a self-piloting plane, no less) to a remote mansion on a hill. He meets other scientists, including a former love interest who claims not to remember him. He also meets Exeter, of course. There are trials and tribulations, because outside of a Calvin and Hobbes comic, scientific progress does not go "boink". Meacham, love interest Ruth, and a pre-Gilligan's Island Professor Hinkley sense whatever Exeter and his white-haired comrades have planned is less than benevolent and try to escape, when the first big reveal comes: Exeter is not of this Earth, and after destroying all evidence of his having been here, whisks Meacham and Ruth aboard his flying saucer. A brief science fiction version of the wash-and-brush-up scene from The Wizard of Oz takes place, a process where Cal and Ruth's skeletons are revealed to the audience, because the two humans would not survive the atmospheric differences of Exeter's homeworld, Metaluna.
Metaluna is reached, but what was once a thriving, advanced civilization is reduced to radioactive ruins. Exeter, it turns out, was seeking aid from human scientists in an attempt to help out in Metaluna's war effort. Hostile outsiders (who we never meet, though we see their ships and the enormous space rocks they lob at the planet) have been ceaselessly bombarding Metaluna, their intentions antagonistic but never really defined.
Exeter presents the humans to The Monitor, a Metalunan leader, but as Thomas Pynchon might point out, it is Too Late. The original plan (which might have been some kind of planetary shield) has been dispensed with. Whatever is left of Metaluna's people will flee to Earth (wait, what?). But no matter; the bombardment continues, and the Monitor is killed. Exeter decides to help the humans escape destruction, and is critically wounded by a hideous, insectile Mutant in the process. They are able to flee just in time to witness the total destruction of Metaluna.
Exeter grants Meacham and Ruth their freedom once they return to Earth, but with his flying saucer out of fuel, winds up crashing into the ocean.
And the movie ends.

Why is he telling you all this, those of you who bothered to continue reading?

Well...
It's odd, but as soon as they enter into the Larger World or Underworld, or Tomorrowland or whatever you wanna call it... they have to leave. Most of what goes on takes place on Earth. The space journey and visit to Metaluna seem truncated. Exeter points out ruins that used to be places of importance, but that's about it. And then bombardment, Mutants, and so on. Our humans have learned much, but a whole planet and its people have been wiped out. Chances are Meacham could reverse-engineer an interocitor, but anyway.

In Explorers... no sooner do the kids meet the aliens on their spaceship... they have to leave. This time, it's because the aliens themselves are children, and the hulking green monstrosity that lumbers in to bellow at them is their dad, really pissed at them for "borrowing" his ship. The human kids go home, and the Thunder Road is lost to the waves, but chances are they could use what they learned to build another ship and go see their alien friends again.

In Tomorrowland... they reach Tomorrowland... but it's not so shiny anymore, and here's where I should have watched the movie a second time, but to wit, two former TV doctors have a fistfight, the clever android sidekick sacrifices herself, and the means to find and recruit more potential Tomorrowland Imagineers is put into practice.

There are probably other examples out there. Maybe even a few predating This Island Earth.