The music came from the drizzle. Witty songs of parochial eccentricity writ large and delivered from within a giant papier-mache head. Frank Sidebottom, the fantastically strange pop star created by the late comedian Chris Sievey, was odd in a uniquely British way. Lenny Abrahamson's Frank, based loosely on the experiences of his former keyboard player, Jon Ronson, makes the man in the mask American, but it reinvents the reality in line with Sievey's unpredictable spirit.
Michael Fassbender plays Frank from inside the mask. Domhnall Gleeson takes on the guise of Ronson. His character, Jon Burroughs, is a commuter-belt drone, dawdling over writing awful songs about surburbia, until he gets a call to come and play keyboards with Frank's band. They're punky and noisy and a pain in the arse for anyone who wants a quiet drink, but they have something. And the something is Frank.
The band decamp to Ireland to write and record an album, where Jon learns that he is not going to be making meat-and-potatoes rock. Frank has invented a new musical scale. Frank wants the band to craft their own instruments. Frank can tell if someone is thinking in the key of C at the wrong time and will clout them for it. Frank will inspire new truth in your soul. He is Captain Beefheart, wringing hours of practice out of his followers, expecting complete adherance to a musical ethos that might be born of insanity.
Tensions rise, Jon and the band's grouchy theremin player, Clara (Maggie Gyllenhaal) wrestle for control over their lead singer. Jon wants Frank to write music that sells. Clara is worried that the pressure will push Frank over the edge. It's hard to tell how Frank feels about any of this. He occasionally describes what his face is doing ("Lips pushed together, as if to say 'Enough frivolity'"), but he wears the mask throughout.
If there's much in Frank that relates to reality, then Ronson (who co-wrote the script) is being tough on himself. Jon is ambitious without realising what his ambition is for. He worships Frank, but assumes that songwriting talent comes from the misery and hard-won experience of his mental health issues. Jon can't accept that Frank might just be good at writing songs. The film plays with our assumptions about the mythology of the pop star. Gleeson's character is constantly looking for his inspiration, but he's never quite on the right wavelength. He is the film's source of disaster, but his disasters never make for a catchy tune.
For a film that champions talent that takes risks, Frank can sometimes feel a little too conventional. The real Sidebottom's wayward genius would be a hard fit for any story arc, but Frank does a good job of dipping into surrealism and pop in equal measure. Fassbender proves a compelling frontman, even when hidden. Gyllenhaal is deliciously sour as Clara, perhaps the one character who realises that an oddity like Frank can't survive too long in the modern world.
Frank debunks the mainstream ideal of what music should be – something catchy, easy to sing, likable. The music, avant-garde rock written by Abrahamson regular Stephen Rennicks and recorded live by the band, is spiky, abrasive and extremely hard to predict. You imagine Sievey would have appreciated that.
• Watch Michael Fassbender in the trailer for Frank here
