Frank is a rare tragicomic masterpiece, one that will surely divide audiences. Jon (the wonderfully endearing Domhnall Gleason; next seen in J.J. Abrams' forthcoming Star Wars: The Force Awakens) is a young office worker who writes songs in his spare time. He adores music, and dreams of an artist's life. His silly songs display a true creative zest, even if the final product might not be Rick Rubin's cup of tea.

Jon stumbles into a chance to play with Frank (Michael Fassbender; Prometheus) and his band, the name of which is intentionally unpronounceable. Frank has a peculiar trait: He wear a large fake plastic head, an over-sized mask concealing his face. And he never removes it. Jon accepts Frank-- only to find himself dragged into this madcap world as the band hits the road in their cramped retro minivan.

As the titular Frank, Fassbender is at the top of his game, aggressively playing down his movie star baggage in the few short scenes in which he's unmasked. Even in the rawest moments of Steve McQueen's Shame, Fassbender was never this painfully vulnerable. The character was inspired by Frank Sidebottom (a British cult music icon who really wore a fake plastic head), as well as oddball music legends such as Daniel Johnson and Captain Beefheart.

Frank is a stellar portrayal of the creative peaks and valleys of a working group of musicians. The fights. The writers block. The meddling outsiders. Every nuance feels right. This is unquestionably the best band movie I've ever seen. Sorry, A Hard Days Night. The cast is rounded out by terrific supporting performances from Maggie Gyllenhaal (The Dark Knight) and Scoot McNairy (Killing Them Softly).

It's the little details along the way that add up beautifully in a script co-written by Jon Ronson (who also authored The Men Who Stare At Goats) and Peter Straughan. Ronson, a Brit-writer who actually lived a version of this story, albeit a less tragic one. It all started with Ronson on a short notice gig, playing keyboards for the real Sidebottom.

The thing that makes Frank an object of fascination for the hipster show business types at SXSW is the head, and the mystique that surrounds it. They've seen a few garbled YouTube videos of Frank but nothing more. It is that surreal fake head that draws them to him.

Sadly, that head is the manifestation of Frank's crippling mental illness. When we see his real head, he's not the pulsating, rock-god artiste that we all imagined. Instead, Frank is a broken and wounded soul, using music as a form of therapy. It's only when he's creating his art that he's truly at peace. Whether or not Frank was aware of that is irrelevant. He just wanted to make music.

The trailers highlight the comedic moments, of which there are many. But the film works best when it treats these characters with true poignancy. This is a far more thoughtful work than the whimsically misleading, faux-Wes Anderson advertising campaign would have you believe.

Skip the trailers. They'll only spoil jokes and give a false impression of the film's tone. Frank doesn't give a s*** if you enjoy yourself, a statement that could apply to both the character and the film.