Undoubtedly one of the strangest movies headed our way this year, Frank is a biopic not of Cheshire-born comedian/musician Chris Sievey, but of his comic persona Frank Sidebottom, who, in the '80s and early '90s, made regular appearances on North West TV, Top Of The Pops and BBC Radio, always wearing a huge fibreglass head.

Not strange enough for you? OK, get your head around this...

"It's set now and it's really not Frank Sidebottom, it's a whole mix of people like Frank," explains author/screenwriter/documentary maker/journalist Jon Ronson (The Men Who Stare At Goats, The Psychopath Test), who played keyboards in Sidebottom's band in the 1980s.

"We fictionalised it. We drew from people like Daniel Johnston, Klaus Kinski, Captain Beefheart and The Shaggs, people who were too odd to ever make it in the mainstream."

Ronson and Goats screenwriter Peter Straughan wrote a hugely ambitious, time-hopping screenplay that "would have cost, like, 100 million". Then Film4 suggested Lenny Abrahamson (What Richard Did) to direct, and the Irish filmmaker helped crystallise the script.

"What I did, I think, is get to the essence of the story," he says, pointing out that the finished script spans just over a year of Frank's life.

"We just got very interested in all those great stories about mad album recordings where bands took themselves off into the wilderness and gradually ate themselves alive. We mined that for comedy, but also for pathos and tenderness. A big part is the journey of Jon, played by Domhnall Gleeson, who comes into the middle of this functioning, albeit mental, world and disrupts the group."




But the big story, of course, is the man beneath Frank's oversized head – Michael Fassbender. "I always thought the challenge of wearing a big fake head would attract someone," says Ronson. Abrahamson, meanwhile, insists Michael met said challenge.

"What he's doing here is so physical," the director explains. "The most expressive weapon in any actor's arsenal has been taken away from him, and yet he creates this real character. You need serious charisma to do that. Michael subtly heightens his movements, works his voice... and he's very comically inventive."

But does he remove the head?

"I think it would be profoundly wrong to answer that," says Ronson. Which doesn't stop Total Film from asking the same question to Abrahamson. "I would have to kill you if I told you the answer," he fires back. "People will just have to wait to see the film."

Frank is currently showing at the Sundance Film Festival. You can read our reaction here.

Frank opens in the UK on 9 May 2014.