[Paul] McCartney was still wrestling with the comparison between the two bands [the Beatles and Wings]. A few months earlier he had commissioned veteran sci-fi author Isaac Asimov to write a screenplay. “He had the basic idea for the fantasy, which involved two sets of musical groups,” Asimov recalled, “a real one, and a group of extraterrestrial imposters. The real one would be in pursuit of the imposters and would eventually defeat them, despite the fact that the latter had supernormal powers.” Beyond that framework, McCartney offered Asimov nothing more than “a snatch of dialogue describing the moment when the group realised they were being victimised by imposters.” Asimov set to work and produced a screenplay that he called “suspenseful, realistic and moving.” But McCartney rejected it. As Asimov recalled, “He went back to his one scrap of dialogue out of which he apparently couldn’t move.”
That is from Peter Doggett’s excellent You Never Give Me Your Money: The Beatles After the Breakup.