Imagine a band where the singer is so painfully shy and awkward that he must wear a giant papier-mache puppet head — not only on stage, but pretty much all the time. That's the premise of "Frank," starring Michael Fassbender under the mask; a story loosely based on the beyond-cult indie musician Frank Sidebottom (aka the late Chris Sievey.)

It's another chapter in the myth of mental illness as pure rock 'n' roll — see Daniel Johnston, Iggy Pop, Syd Barret, Captain Beefheart, et al. The film starkly contrasts Frank's idiot-savant freedom with that of his careerist keyboardist Jon, (Domhnall Gleeson), who wants to rein in the band to be "more likable" and play the industry game at Austin's legendary South by Southwest festival. Frank eventually collapses into a fit, shrieking at Jon "You make music sh-t!"

"Frank," which opens this weekend, is a wildly offbeat and amusing film, but while it differs in its puppet-head particulars, it treads an incredibly common path for this sort of musician-as-head-case story.