If Theo James had known more about Divergent, he might've blown the audition.
"It was serendipitous," he admits. "I happened to be in LA for something else. I went in, not knowing much about it." Only afterwards did he read Veronica Roth's hit Young Adult novel - and only when he realised the film's producers were interested in him. "Otherwise I wouldn't have bothered!" he laughs.
All of a sudden the 29- year-old Brit is Hollywood's latest hot property. After just a week and a half on release in the US, Divergent has already taken close to $100 million. Trade paper Variety positioned him as "the next YA obsession", following along the lines of Twilight's Robert Pattinson and The Hunger Games' Liam Hemsworth.
And just to add spice to the situation, he's currently dating his Divergent co-star Shailene Woodley.
As he kicks back in London's Soho Hotel, dressed in black jeans and grey cardigan, James is certainly handsome enough to cause young adult hearts to flutter: brown eyes, stubble-clad square jaw and a look that once led a paparazzo to mistake him for James Franco.
His Divergent producer, Lucy Fisher, claims he has "that 'I can get hurt thing' that James Dean had" - though in person he comes across as more cheeky lad than wounded soul.
Rather like its YA rival The Hunger Games, the story is set in a dystopian future where political oppression is the norm.
In a war-ravaged Chicago, currently fenced off with a giant wall, society has been re-moulded into five factions based on personality types: Abnegation, Amity, Candor, Erudite and Dauntless, the warrior-like, adrenaline-pumped peacekeeping schism which James' beefy character, Four, belongs to.
Each teenager is required to choose a faction, which James claims is "reminiscent" to the Nazis' own Final Solution during the Second World War.
"It's based on purity," says James. "This idea you have to be pure. A Divergent isn't pure. It's someone of mixed mental capacity. They don't fit into one group."
While Woodley's heroine Tris selects Dauntless, where she is mentored by James' character, tests have shown that she too is Divergent.
Much of the first film is taken up with Tris's training (not to mention making eyes at James) but rebellion and revolution - again like The Hunger Games - is brewing.
"You get the idea at the beginning that the concept of this faction system is breaking, and there's disenfranchisement within the society," James says.
As for Four, he undergoes his own awakening, something James can certainly relate to.
He's already done a stint of pre-release promotion at a Las Vegas Comic-Con, seeing the Hollywood machine close up.
"You have this weird juxtaposition - the glamour is fun, and you're being shepherded around and you're doing all these interviews. But then there's also a ridiculousness of it. The celebrity-ism, I guess."
He took along his brother, who runs a bar. "He was standing outside in a Liverpool [FC] shirt, having a cigarette, going 'What the f*** is this?'"
Born in Oxford, the youngest of five and the son of an NHS worker and a business consultant, James is the family's only actor.
"I think I was the one that was always going to do it because I had the licence to," he says, noting that his parents had probably done all their worrying about his older siblings.
Still, he didn't immediately consider it as a possible career. "I thought about doing it at 18," he says, "but I wasn't ready or good enough."
Instead, he studied philosophy at the University of Nottingham, and it was only when an ex-girlfriend started auditioning for drama schools that James followed suit.
He wound up at the Bristol Old Vic Theatre School, following the likes of Daniel Day-Lewis and Jeremy Irons, before starting the endless round of auditions. In 2010, he snagged a role in Woody Allen's You Will Meet A Tall Dark Stranger. Then came a memorable bit-part in Downton Abbey as the Turkish diplomat who courted Lady Mary and, sensationally, died while they were having sex.
Since then, James has featured in US detective show Golden Boy, though his biggest role was as the tour rep bully in The Inbetweeners Movie, which he estimates is "one of the things I get recognised for in Britain the most". That, of course, will all change with Divergent.
Judging by its early box office success, Roth's next two books in the series, Insurgent and Allegiant, are almost certain to go before the cameras, which means James will be back as Four.
In the meantime, he's been careful enough not to repeat himself. "Doing a big YA thing, I wanted to do a) something very different and b) that would push myself," he says. He'll be seen in an old-fashioned Hollywood drama, Franny, with Richard Gere and Dakota Fanning, followed by a key role in a much-anticipated take on Martin Amis' cult novel of millennial angst, London Fields, playing the "uptight British banker" Guy Clinch opposite Amber Heard. It is a book that has already defeated the likes of David Cronenberg and Michael Winterbottom, who both pulled out of directing it, and Amis adaptations have a tendency to falter on screen. But for James it represents yet another major stepping stone. How on earth is he keeping his head together?
He shrugs, claiming that "gradually making steps" has helped him acclimatise. Yet even he can't shake off feelings of superstition. "Who knows? You may speak to me in five months and I will be out of work."
Divergent opens tomorrow