At first glance, Frank seems like twee hipster bait. It's about a struggling songwriter. Tweets flash onscreen like in a millennial episode of Pop-Up Video. It treats Austin—and specifically South by Southwest—like El Dorado. A pixie-haired Maggie Gyllenhaal plays synth. Oh, and its star spends the entire film wearing a gigantic fiberglass head modeled after an early Max Fleischer cartoon character, complete with saucer eyes.

Yet director Lenny Abrahamson dodges contrivance to emerge with something truly special: a comic drama forged at the intersection of mental illness and outsider art. Frank deftly moves between humor and melancholy while examining messianic artist worship. 

The great Michael Fassbender plays Frank, a character inspired by the stage persona of musician Chris Sievey, who donned a similar head when performing as Frank Sidebottom. (Jon Ronsom, who wrote the screenplay with Peter Straughan, played in Sievey's band.) We're first introduced to Frank onstage, when dweeby hack Jon (Domhnall Gleeson) is enlisted to play keys for Frank's band, Soronprfbs. Amid a cacophony of noise-pop hooks, Frank flails around with the vigor of David Byrne being tased, spouting nonsense lyrics—"fiddly digits, itchy britches, I love you all"—to an empty room.

Captivated, Jon agrees to join the band as it records its masterpiece. Whisked away to a rustic Irish cabin, he's initially puzzled by the cult of personality surrounding Frank. He also draws the ire of Clara (Gyllenhaal), whose overprotectiveness of Frank borders on sociopathic. But Jon eventually becomes enamored with Frank, and he secretly posts their rehearsal footage online, which takes them to SXSW—and to a series of meltdowns. 

Fassbender has become one of his generation's best actors. He can play a supervillain in X-Men and a racist monster in 12 Years a Slave, and he can show vulnerability (Shame) and charm (Inglorious Basterds). Here, forced to hide his striking smile, he conveys Frank's alluring charisma, artistic genius and openheartedness through his body language. His nervous tics and erratic movements gain gravity when it's revealed Frank was recently institutionalized for unnamed reasons. When paired with his droll surfer voice—which, when singing, evokes a cross between late Morphine frontman Mark Sandman and the National's Matt Berninger—it's both goofy and startling. 

But Frank is much more than a movie in which Michael Fassbender dons an oversized helmet. It's about the lust for artistic recognition and the toll of sudden fame. It's heavier than a comedy about a gibberish-spewing guy in a giant head ought to be, but that's what makes it a thing of heartbreaking, oddball beauty.

Critic's Grade: B+

SEE IT: Frank is rated R. It opens Friday at Living Room Theaters.