A possible plot for a part 4 of Back to the Future would be as follows: Marty McFly and Doc Brown meet again in the year 2025, when Marty’s son is in trouble with the law. Doc offers Marty the chance to travel back in time to prevent his son from making a mistake that will change his future. However, upon reaching the year 1985, they realize that someone has altered the time line and have created an alternate reality where Biff Tannen owns Hill Valley and is in control of the time machine. Marty and Doc must find a way to restore order and return to their original present, before Biff discovers and eliminates them.
This, however, seems to never take place, after an interview that Michael J. Fox gave with Variety:
fox considers that the work that the director did robert zemeckis in collaboration with the scriptwriter Bob Gale it is irreplaceable.
“I’m not a fan. I have already been paid. But that doesn’t mean I think it’s a good idea.. I do not think that it’s necessary. I think Bob and Bob have been very smart about it. I don’t think it’s necessary to restart it because are you going to clarify something? Will you find a better way to tell the story? I doubt it”.
“I’m sure someone thought of it (a fourth film of Back to the Future) . But I was in the early stages of Parkinson’s at the time., so I don’t know if I would have wanted to assume it. Right after the third part did well, there might have been talks about it, but i never got involved in itFox added.
However, Doc, played by the classic Christopher Lloyd, has another vision of things:
“I would love to do a sequel, but I think Bob Zemeckis and (producer Steven) Spielberg felt they had told the story in all three episodes. But if someone has a brilliant idea that justifies a fourth movie it could happen”.