You don’t need to be aware of the fact that Frank is loosely based on a real life musician, Frank Sidebottom, and author Jon Ronson’s (who co-wrote the film) brief stint as the keyboard player with his band (the Frank Sidebottom Oh Blimey Big Band) to enjoy the quirky film. In fact, it isn’t even really relevant except for perhaps some insight into the screenplay, where you can find hints of film dialogue in this article by Ronson over on The Guardian.
If this film were a true story, it would be tragic to know the character Jon Burroughs (Domhnall Gleason) actually behaves how Ronson himself may have during a stint in the band. But I presume he is a more loose construct because Burroughs is a maddening character with selfish motivations and guileless irresponsibility. All he wants to do is make music successfully. So when Burroughs realizes there is a momentary gap in The Soronprfbs lineup, he offers his services. Then, he somehow ignores this disastrous first gig, and agrees to record an album with the band, taking near permanent leave from his desk job to see it through.
He does this all because he is inspired by Frank (Michael Fassbender), the musical wellspring and bandleader of The Soronprfbs, who nonchalantly wears a custom papier-mâché mask over his head for the performances… and for showers. The man never takes off the mask leading to questions about his mental state (by the viewer at least). The loyal followers at Frank’s side are Clara (Maggie Gyllenhaal) who seems self-assigned to guard him, Don (Scoot McNairy) who manages the band, Nana (Carla Azar) who plays drums and Baraque (François Civil) the guitarist for the outfit. Their motivations for being in the band with an un-pronounceable name aren’t fully explored but these kindred social outcasts happily follow Frank, comfortable in their self-imposed exile.
Sacrificing an unknown personal fortune in order to help the recording process, Burroughs never manages to mesh with the eccentrics he shacks with. As Burroughs’ ambition rises, the (non-Frank) group’s distaste for him grows yet naively he persists within this hostile environment. Through the surreptitious behind-the-scenes videos Burroughs posts on social media (somehow without the band’s knowledge), he ends up commandeering the managerial role for the group and proceeds to further his attempts at fame via sharing the genius of Frank (and his own role in the band) with the rest of the world. The Soronprfbs receive an invite to play South by Southwest, forcing them from their shell. (I wonder how Frank got through immigration; what picture is on his passport?) Things only go downhill from there.
Within the group’s dysfunctionality resides the film’s dark humor, particularly in the scenes where Burroughs performs a song he wrote for the band before Frank joins in or when Frank presents his most likeable tune. But, while reaching bigger audiences is clearly something Frank wants, his personality issues prevent the band from attaining the acceptance Burroughs is striving for. Desire fills his fake head, crushing Frank’s mental walls, releasing the more serious side of the film. It is in this latter act that Burroughs redeems himself and Frank could possibly become content again. But until that point, Clara’s fervent disdain of Jon is the same read the audience should have of him.