Whether the word was "cherishable" or "perishable" was a little hard to make out, on account of the man always wearing that big papier-mâché head. But Frank, the man inside the head, sees something special in a budding young musical mollycoddle named Jon (Domhnall Gleeson), and decides to hire him. Frank, an inscrutable pied piper of art-rock obscurity, has his ways. Is it sort of a spoiler to declare that the title character in director Lenny Abrahamson's dark comedy, whose face we almost never see, is played by Michael Fassbender? Maybe, but it'd be worse to go through the movie wondering, "Who is that?" Better to know and to anticipate the long-delayed reveal; contrary to some opinion, the most stirring Fassbender stuff, anatomically, is in his eyes. Whether we're holing up in the woods to make a record, or watching Maggie Gyllenhaal surpass typecasting as a severe, theramin-wielding bandmate, or hoping they don't choke during an important South by Southwest show — Frank's voice and posture, the way the head weighs him down, is always central. Though packaged for relative ease of consumption, Frank does manage to investigate the frontier between indie quirk and mental illness, the volatile combination of tortured soul and personality cult. Mystifying, demystifying, it seems a little at odds with itself, but then so does Frank.