Jon (Domhnall Gleeson) is a slightly dorky guy on a beach, free-associating song lyrics, trying to hit on something that sounds like music. Instead he stumbles upon the scene of a suicide attempt, a raving lunatic being hoisted out of the sea. The hypothermic man is taken away by ambulance, leaving his bandmates scratching their heads around their van – how will they play their show tonight without their keyboardist? But wait! Jon plays keyboards! So he shows up that night to a gig and finds that this group isn’t just some unknown indie band, it’s an ultra-unknown and perhaps unknowable avant-guard indie band that’s lead by Frank (Michael Fassbender), an enigmatic man never seen without his papier-mache head, and Clara (Maggie Gyllenhaal) a super angry woman with bad haircut and a grudge against her theremin.

Back at work the next day, Jon’s life seems even more dull and meaningless than ever. His latest sandwich is the highlight of his twitter feed. So when his phone rings and it’s the band asking him to join them again, he jumps at the chance. Only this time it’s not for a gig, it’s for an indeterminate recording session in a remote cabin in the woods. At first Jon is elated to be part of Frank’s charismatic genius, believing that Frank can summon untapped corners of Jon’s own musical aptitude, but things are not easy with the music or between the band members. Ever the optimist, Jon gamely decides that this experience will substitute for the traumatic childhood he never had, fuelling and giving direction and “theme” to his songwriting.

Or so he thinks.

This movie never does what you expect it to, even after setting up parameters pretty much right away indicating  that this is not exactly going to follow a straight and narrow path. It’s quirky and weird but also kind of sombre and introspective. It doesn’t hide behind easy choices, and as a device, the papier-mache head actually seems to unmask people’s true feelings rather than obscure them.

Michael Fassbender gives a surprisingly solid performance from behind his huge head.  He plays that aloof, outsider rocker genius thing awfully well (almost as well as Maggie Gyllenhaal does the sour bitch, and that’s saying a lot). But the movie debunks\demystifies the glam-nutbars in a band thing, and Jon is soon learning just what it means to be the only straight one around.