The "plot" takes place in an alternative reality where America's split into separate countries. A complicated and bloody civil war is raging. To rally support for the government, a "benefit" concert is to be held with jailed singer "Jack Fate" as the headliner, played by no less than Dylan himself.
Jack is a way past his prime rocker who at one time wrote music that once resonated with people, but his words evolved into pointless artifacts of a bygone age. There's a deep cynicism in the movie on whether "rock" music can ever change anything. Is it all pointless nostalgia. Does Dylan feel that way about his music? Or just other people's music? Who knows?
Supporting characters are symbols and motifs from Dylan's career. Jeff Bridges (Tom Friend) is the nefarious "rock critic" trying to reveal Jack Fate as a fraud (only in Dylan's universe would a rock critic be the arch-villain). John Goodman (Uncle Sweetheart) symbolizes show business schmaltz. Luke Wilson plays a disciple of Jack's with little to say in his own right. Some of the scenes work and some don't. My favorite features the characters musing on the meaning of Jack's music, a nice meditation on the subjectivity of interpretation.
Dylan's remote performance prevents the film from going beyond mere symbols and fragments. Some have suggested the movie originated from Dylan's "Desolation Row" or "Lily, Rosemary, and the Jack of Hearts." Possibly.
Like Dylan's 1978 film Renaldo and Clara, the characters are distant and meandering. Music proves a saving grace. Watch it at least once. Non-Dylan fans beware.