The room is dim. Four musicians tinker with their instruments as a fifth, the front man, walks onstage. A slight but noticeable crescendo accompanies his entrance. He is tall, with a strong build. Atop his broad shoulders rests a large fake head wearing a nondescript expression. He feels for a cable around the microphone stand and connects it to the head. As he begins a cult-like incantation over the increasingly chaotic froth of sound, we can’t help but expect an event. But at the very moment we think the scene will meet our anticipation, the sound system overloads and sparks fly out from the amplifiers.

This moment sums up “Frank” decently well. At first glance it feels like it should be an event, but ultimately the film exists on a far smaller, more intimate scale. Although its larger narrative scope feels meandrous, its off-center nature is often darkly hilarious. Director Lenny Abrahamson and co-writers Jon Ronson and Peter Straughan play with a frenetic, emotional spectrum, jumping sometimes very sharply between bleak and bright beats.

Domhnall Gleeson is our proxy as Jon, an office worker and aspiring musician. The film’s opening sequence works masterfully to establish his character. We see him stare out at the ocean, mouth closed, as his voice makes stumbling attempts at songwriting in the soundtrack. As Jon walks through his town, he continues to throw these ideas at the fourth wall to see what sticks. Talk about “show, don’t tell.”

By cinematic happenstance, Jon meets Don (Scoot McNairy), the manager of a little-known band with the barely-pronounceable name “Soronprfbs.” After their keyboard player’s recent suicide attempt, the band has an opening, which Jon rapidly accepts. Off they go into the woods, to a secluded cabin where they spend nearly a year recording what aims to be the band’s masterpiece. Jon schemes to make it their big break, and the increasingly ridiculous hashtags he affixes to tweets about the band’s progress are a welcome humorous spice.

“Frank” moves meditatively through its 95 minutes. Abrahamson understandably spends most of his time, and ours, focusing on the titular character’s eccentric creative process. The role requires much of Michael Fassbender, whose recognizable face is covered for nearly the entirety of the film. When we finally do see beneath the giant papier-mâché head, the effect is neither shocking nor comforting. The transition is seamless thanks to Fassbender’s commendable consistency and commitment. He carries Frank’s enigmatic persona with physicality, expertly conveying emotion through the slightest changes in body language.

The head’s appearance remains unchanged, but in the slightest tilt of his shoulders, Fassbender reveals a devastating shift in feeling. He sinks deep into Frank’s elusive demons, and adds affecting duality to the mysterious character. The film also plays with the difficulty of understanding the alleged genius, as Frank starts literally describing his hidden facial expressions. Fassbender’s deadpan earnestness is so wonderfully ridiculous it keeps you engaged on hilarity alone.

Gleeson is equally compelling in his perhaps too-familiar role as a fame-hungry everyman, but it’s Maggie Gyllenhaal who cuts deepest. As Clara, the band’s foul-mouthed synth and theremin player, she easily owns all of her scenes, on multiple levels. Her acting is fittingly sublime for a character who obsessively controls nearly everyone around her. She’s formidable on both sides of the script and her absolute commitment to getting what she wants manifests in the film’s funniest and most surprising scene.

“Frank” works best when it plays up its own quirks. But for its ending, which all too dismissively sweeps an important issue of mental illness under the rug, the film successfully conveys its storytelling. The denouement fails to fully acknowledge this very serious undercurrent running throughout, and in so shruggingly loses some of its heft. That lapse isn’t enough to offset the film’s unique charm. Thankfully, the film relies more on its leads and mood than on the resolution of its deeper tensions. “Frank” drops a few threads too abruptly, but like any good performer, it leaves the audience wanting more.

Nathan Frontiero can be reached at [email protected].