The late, great singer Ronnie James Dio reckoned that every band needed to be a democracy led by a dictator. In Frank you get three for the price of your ticket: the man himself (Fassbender), who's hidden inside a papier-mâché head; his nurse/jailer Carla (Gyllenhaal) and power-seeker-in-waiting Jon (Gleeson). It's just a small mercy that they don't have a roadie.

Jon is an affable desk jockey who's convinced that the world needs to receive his gifts as a songwriter. It doesn't. That said, nature abhors a vacuum, so when Frank and Carla's unpronounceable outfit Soronprfbs lose their keyboard player, the Universe speaks and puts Jon in their path. And so begins a strange, bank account-draining (mis)adventure involving the making of an album, the power of social media, a once-in-a- lifetime opportunity and a quest to get to know the man behind the mask - without Carla resorting to murder.

From This Is Spinal Tap to Dig! to Anvil: The Story of Anvil and Bad Brains: A Band in DC, we've had many a great chronicle of group dysfunction, and this offbeat treat - loosely inspired by co-writer Jon Ronson's time in outsider artist Frank Sidebottom's band - deserves its place in the cult music movie pantheon. Like Soronprfbs' music, Lenny Abrahamson's film will not leave you indifferent: some will rank Frank among their hits of 2014, while others will fold their arms in high dudgeon many times. Both camps should be able to agree, however, that the performances are excellent, with Fassbender showing that the difference between an actor and a film star is that one would wear that head for a whole movie and the other probably wouldn't. After a while, you even forget he's got it on.

There's a suspicion here that there were more quality japes and scrapes to be had from the storyline, but perhaps they would have diminished the power of the finale, a real eye-opener that equals the best moments in Abrahamson's Adam and Paul, Garage and What Richard Did. While you won't be able to hum any of Soronprfbs' 'tunes', you'll be thinking about the ending for a long time afterwards. What's missing in melody is made up for in heart and soul.

Harry Guerin