Domhnall Gleeson plays Jon, a naive would-be songwriter who rather abruptly – and randomly – is asked to join an avant-garde band called "Soronprfbs", led by a friendly but thoroughly mysterious frontman named Frank (Michael Fassbender in a bit of surprise casting) who hides his face behind an enormous papier-mâché head.

Does this sound like insufferable quirk? At first, it is. Jon's gee-whillikers attitude towards Frank and his surly band (including Maggie Gyllenhaal) and the lighthearted score spell out doom. For a while, you can see where the story is going: With Frank showing genuine songwriting skills beneath his many eccentricities – something apparently only Jon can notice and encourage – you can imagine the band slowly coming together, Jon's own musicianship being appreciated, and everybody having a jolly good time.

If this film were called Jon, then such a scenario might well play out. But this film is called Frank, and while I won't give anything away – although there are not exactly any surprise twists – I can tell you at least to stay with it, for Frank almost imperceptibly transforms from the sort of film you're afraid it's going to be into the sort of film you'd hope it would be.

In some ways, the film reminds me a bit of Vladimir Nabokov's experimental novel Pale Fire, in which a dead poet's masterpiece is misinterpreted on an absurd scale by his narcissistic self-proclaimed "biographer". Frank doesn't have nearly as adventurous a narrative structure, but the idea is the same: that as Jon tells Frank's story, he's really trying to make it his own story – and while Frank may be clueless about the whole thing, his surly bandmates can see what's really going on.

After that, whether the film is "about" anything – like whether talent is a natural gift or not, or if insanity is what really fuels creativity – I can't say. There's a certain inscrutability to Frank that makes it hard to explain away in a sentence or two. I can't say that it's a great film, as you still need to pick through a hell of a lot of quirkiness to get to some sort of meaning, but it's still a very interesting one. I'm still thinking about it days later.

To be fair, Frank's – and Frank's – gimmick of the big head is based on a creation of the late English comedian Chris Sievey, who wore a giant head almost exactly like the one in the film. Sievey's alter ego was even named "Frank Sidebottom". (Co-screenwriter Jon Ronson worked with Sievey, who reportedly gave his blessing to the film before his death in 2010.) Anyone who's seen the documentary The Devil and Daniel Johnston will see similarities between Frank and Johnston as well; the two films might make a great double feature.