Yesterday” is wildly implausible, to a degree that makes “Back To The Future” look like a serious exploration of the theory of relativity. It’s a sheer waste of time to ask yourself any of the innumerable questions raised by the macguffin that is the film’s premise. But if you’re willing to suspend your disbelief, it’s a pretty fun romp. That’s my take, anyway: opinions are certainly divided.

Great credit must be given to the cast. Himish Patel’s intense likability makes scenes work that really shouldn’t. Kate McKinnon steals every frame she’s in, as an evil music executive. And Ed Sheeran is believably himself, which is all this film requires. The supporting players range from good to excellent. The weakness is the script.

The rooftop concert in “Yesterday” — one of the film’s many nods to Beatles-related events.

And by “script” I don’t mean the aforementioned motivating plot device (supernaturally powerful solar flares that manage to wipe out all record of the Beatles — including physical objects like recordings and books). No, I mean the love story and the way Jack Malik (Patel) ends up dealing with the results of his having passed off the Beatles’ song catalog as his own. Lily James works hard as Jack’s lovelorn manager Ellie, but there’s not much believable chemistry between them, and the resolution of their story feels shoehorned into the rom-com framework. Pretty much all Jack’s other relationships — with his mentor Sheeran, with McKinnon’s manipulative manager, with his friend and roadie Rocky — are more compelling than his erstwhile romance with Ellie.

The film is at its best when chronicling Jack’s idea of passing the Beatles’ songs off as his own and the early stages of his discomfort with that decision. Patel expertly portrays Jack’s initial giddiness and growing disquiet; I found it impossible not to root for a happy ending for him. And he gets it. I just wish the way that he gets it didn’t feel so contrived.

In musical terms, “Yesterday” posits that the Beatles’ song catalog is powerful enough to launch a superstar today, but it studiously avoids exploring the band’s cultural impact. Apparently the world would look just like it does today, except that Oasis would never have existed and John Lennon wouldn’t have been murdered.

But in the end, it’s pretty much impossible to argue that “Yesterday” is taking anything seriously. It’s simply an enjoyable summer diversion with plenty of Easter eggs for Beatles fans to find.