It might not be intentional (though I suspect it probably is), but the British-Irish comedy-drama Frank plays a game of such meta-textural delicacy that the whole movie couldn't really exist if it hadn't succeeded. To wit, we have here a film that acts as hard as it can like an idiotic quirky comedy from the 2000s, playing every stylistic card it can to add a sense of visual whimsy and pushing its lead actor into a heightened, poppy emotional register that suggests a simplistically likable everyboy hero. And then, right about halfway through, when the charm of it has started to wear out and the goofiness is drifting towards shrillness, the bottom falls out, and we're suddenly watching a surprisingly raw depiction of damaged psyches that deal with the scariness of the real world by acting quirky. In effect, the film is using an overplayed genre as a blind to lull us into expecting all the wrong things, and then when the actual content of the movie is sprung on us, it hits all the harder for it, while also caustically indicting all those quirkfests of yore as unfathomably divorced from human experience. Not bad for 95 minutes' work.

The protagonist is Jon Burroughs, played by Domhnall Gleeson with the spirited can-do attitude of a parakeet. He's toiling away trying to write pop songs based on life he witnesses in his greyed-out suburb of Dublin, leaving all his thoughts unfiltered and married to trivial la-la tunes, and one day, by chance, he meets Don (Scoot McNairy), a member of a very eccentric music group passing through town. They need an emergency keyboardist for that very night, and Jon leaps at the chance to play with real musicians, but the set doesn't last for very long: thereminist Clara (Maggie Gyllenhaal) breaks her instrument and storms off minutes into the first song. But something about Jon impresses the band's leader, Frank (Michael Fassbender), who invites the young man to join as their permanent keyboardist. Nobody else is terribly happy with this, but what Frank says, goes. Which, incidentally includes the fact that Frank wears an enormous papier-mΓ’chΓ© head at all times, and no-one in the band has ever seen his actual face.

Jon's enthusiastic tweeting and YouTubing (annoylingly over-stated with onscreen text - if social media stays an important part of human life, filmmakers are going to have to come up with a more interesting way of dealing with it) about the band's progress over the next 11 months as they toil in the Irish countryside over an album brings them some unexpected prominence, but at the same time, he grows more and more painfully aware that something is not right. Frank's perfectionism leads to endless practicing but no real musical creation, and the interpersonal dynamics within the band are erratic and emotionally broken. All of which is sharpened when Jon's activities bring the band an invitation to America to play in SXSW, and the full depth to which Frank and company aren't actually able to deal with the implications of that start to explode in rather nasty ways.

To clarify one important thing first: while Frank is not the dipshit quirky comedy about magical eccentrics that it looks like, it still has some fairly urgent limitations as a work of cinema. Since the first half of Jon Ronson and Peter Straughan's screneplay is structured as a fake-out that leaves all the thematic and psychological development for the end, it spends a great deal of time revving and very little going anywhere, and Gleeson's bright, smiley performance is frequently the only thing providing much of a shape the proceedings at all. The film clearly things that the situation it's depicting is much weirder and thus more captivating than really turns out to be the case; there's only one joke, and director Lenny Abrahamson's manner of visually staging everything with an eye towards realism doesn't ever let that joke flourish. Fassbender's performance is sweet enough, even with his face hidden, but the rest of the band fade into the background, and Gyllenhaal's featured moments are all reductive and shrewish in a way that benefits neither the character nor the actress.

The film picks up a great deal of steam as it moseys along, and Fassbender's performance gradually deepens and moves from a pleasing embodiment of an indie-film conceit into a surprisingly complex and nervy portrayal of delicate psychology, all using just his body language and voice. Not that those are little things, and his line readings in particular are filled with  layers of feeling and splashes of desperation and fear that are unexpected and alarming and touching all at once. Really, it's just another in a line of great performances from one of the most reliable actors in the world - I doubt very much that anybody would walk out convinced that they'd just seen his new career highlight - but if Gleeson provides the first half of the movie with its spine, Fassbender provides the second half with its insight and humanity, frightening and off-putting though that humanity might sometimes be.

It's still not the case that Frank ever entirely coheres into a unified statement or a clear narrative progression. The ultimate message, that artistic genius is slippery and elusive and maybe not much fun to have or to be around, is a little looser than it should be, and despite how much it grows out of Jon's character arc, the film seems increasingly unsure what to do with him for its last ten minutes or so. It doesn't wrap up so much as it finds a place to coast to a stop. Nobody wants that kind of thing.

Even so, the parts of Frank that work are pretty delightful. The sense of humor is a little forced, but treated with enough deadpan under-emphasis that it manages to be funnier than it maybe ought to be, and Gleeson is a sweet enough lead that his lack of modulation in his set cheeriness throughout the opening acts doesn't damage the film as badly as it might have. And it's always worth watching Fassbender, even just parts of Fassbender. There's enough complexity and thematic insight here that these characters end up feeling more than the sum of their parts even if the film containing them can never quite manage the same feat.