“There’ something wrong with Frank;” the line that perfectly summarises Michael Fassbender’s character in this obscure film of the same name. After a cheerful reception at this year’s Sundance and SXSW festivals, Lenny Abrahamson’s offbeat interpretation of one of pop music’s more bizarre performers reaches cinemas this May.

What began as a first hand testament to Frank Sidebottom who Jon Ronson, now an established author, briefly played with in the 80s, has grown into a fictional account of an unhinged but naturally brilliant musician, inspired partly by the lives of Daniel Johnston and Captain Beefheart.

Ronson, who wrote The Men Who Stare at Goats, pairs up with previous collaborator Peter Straughan (Tinker Taylor Soldier Spy) to craft a screenplay told from the perspective of Jon, a well intentioned but creatively challenged musician. Based loosely on real events, events escalate after a well timed but unfortunate coincidence which sweeps Jon away from his mundane life into that of Frank’s, a singer whose enigmatic weirdness is personified by the large papier-mâché that he insists upon wearing at all times.

The company that Frank keeps is equally trying on his impressionable new companion. Maggie Gyllenhaal is Clara, Frank’s tightly wound and terrifying band mate who finds plenty of opportunities to tell Jon what she thinks about him, which apparently is very little. Then there’s the band’s manager Don, a stereotypical piece of work with a mannequin fetish, played by a wiry Scoot McNairy.

Domhnall Gleeson is Jon, an eager soul whose limited love of music is closely rivalled by that of detailing every moment of his day via social media, tweeting Panini updates and woeful observations followed with the ironic hashtag “living the dream.”

It’s Jon’s social coverage of the band and the making of their album out in the Irish wilderness that cause their popularity to soar, sparking an invitation to Texas and a request to perform at the SXSW festival. Along the way things become unscrewed; Frank’s mental state fragments while his band mates bicker furiously, putting an extraordinary amount of pressure on the looming performance.

Given Ronson’s account of his days as the keyboard player for Sidebottom’s band this is expected to be a dark, if funny film. Early reviews from Sundance and SXSW have been largely positive, with a strong emphasis on the film’s bizarre concept, as well as the fact that the film’s star stays within the head for almost the entirety of the film.

Frank sees Fassbender explore a lighter and more physical role, a refreshing change from his mostly sinister roles of late. Director Abrahamson had said on occasion that the actor grew comfortable with and even enjoyed wearing the head. Even with his name attached to the project however it’s been a tricky idea for people to wrap their heads around, including the cast. Maggie Gyllenhaal originally turned down the role, unsure of the tone of the film and what to expect of Frank and only returning when she saw what the character was really about. On set the cast dealt with their co star’s ballooned accessory by simply pretending it wasn’t there, resulting in a complete dismissal of his condition. It is only through Jon’s wide eyed wonder that the issue is addressed, and even then resolution is far from reach.

Absurdly oversized heads aside, Frank calls to question the importance of popularity and gently mocks the power of social media. Jon craves recognition and the power that comes with talent, whereas Frank becomes as imprisoned by his own genius as his cage like fake head. It’s a challenging role, that relies at times on Fassbender voicing his emotions while at others allowing his physical outburst to speak for themselves.

Steering the story of the papier-mache’d icon is Abrahamson, whose last feature What Richard Did about a boy dealing with an accidental crime met favourable response, won multiple awards and secured its star Jack Reynor as Hollywood’s new poster boy. His next project will be The Room, an adaptation of Emma Donoghue’s bestselling novel about a boy raised in a shed, and so emotional confines appear to be his forte. Like Fassbender this a lighter step in his career, allowing humour although dark to navigate the story through Frank’s emotional unravelling and towards the imminent career defining performance.

For someone the concept of Frank may be too obscure to handle, this certainly is a portrayal of a star like no other. For others, the bizarre nature of the story, seen through an outsiders eyes just like our own works favourably to create a fitting account of the pressures of a wanting industry on an unsure performer.