What is a word for a hidden story beneath the main one?

It's a lot more complicated than my title seems... I've been trying to find a word that describes this specific situation.

For example, there is the story "The Wizard of Oz" and then there's the re-telling of that story, "Wicked". Where the audience sees the point of view flipped, and now everyone who seem good is now bad and vice-versa. Would it just be a re-telling? Because I'm specifically looking for a word ( that's not really Conspiracy, because where I'd like to use it the "Conspiracy" wouldn't be one because it was true and confirmed within the story) that deal with situation that there was the "REAL STORY" under the first one presented.

"Wicked" isn't the official prequel to "The Wizard of Oz" but it needed that story to create this fan made " This-Is-The-Real-Story-Going-On-Here " one ( or " This-Is-What-Really-Happened" story ). What is that called?

I've basically come up with jack squat to figure out if there is a word or a small phrase to describe this, the closest word I've found ( besides Conspiracy, but that gives off the wrong connotation and overall vibe ) is Arcane. And ... That kinda barely fits the way I understand it. Is it really just called a "Re-Telling" and that's just it?

Edit:

I'd just like to point out that "subplot" is also not the word I'm looking for

I think you might mean "subtext." See the article on Wikipedia, which contains other ideas you may wish to use instead. https://en.wikipedia.org/wiki/Subtext

It's a secret history or shadow history.

From Wikipedia.

A secret history (or shadow history) is a revisionist interpretation of either fictional or real history which is claimed to have been deliberately suppressed, forgotten, or ignored by established scholars.

An example they give of a shadow history of a fictional world is:

"Philip José Farmer's The Other Log of Phileas Fogg reinterprets Jules Verne's famous tale with the assumption that in fact Fogg was the immortal foster child of a race of hominid aliens known as the Eridani, and that his travel around the world was part of a secret mission on their behalf."

And an example of a shadow history of the real world:

"Alexandre Dumas' last major work, The Knight of Sainte-Hermine asserts that it was the novel's protagonist who killed the British Admiral Horatio Nelson and that the true circumstances of Nelson's death were kept secret for reasons which form part of the book's plot."

I don't know whether just telling the same events from a different point of view (like The Wind Done Gone) qualifies as a shadow history, but I believe that Wicked introduces enough new revisionist background that it does.