Sam Worthington's latest role as a Mossad agent is probably his most thoughtful to date – but then he's always had a sensitive side. Matt Mueller finds out

Sam Worthington would like to make one thing very clear. His role as a taciturn, tormented Mossad agent in John Madden's The Debt is not part of some concerted campaign to leave the brawn behind and enter a more cerebral domain. The Debt – and its immediate predecessor on Worthington's CV, Massy Tadjedin's Last Night – could be viewed as an attempt by the 35-year-old actor to come across as a more thoughtful male star than the hunky action man who rampaged through Terminator: Salvation, Clash of the Titans and, to a lesser extent, Avatar. But he's having none of it.

"There's no grand plan, mate," he says in his brusque, no-nonsense Antipodean fashion. "I think my agents have a grand plan but I have final say, so... People keep saying these are smaller movies. Yeah, the budgets are smaller, but my job doesn't really change, which is to strive for truth in imaginary circumstances."

The Debt, he explains, came about before Avatar and Terminator: Salvation had made his name, when Madden flew to visit him on the New Mexico set of McG's failed effort to reboot the Terminator franchise. "I thought, 'any man who's willing to fly to the home of green chilli and weaving is a man that I'll give my attention to'," the actor grins. "He'd seen Somersault and there was a similarity in the way the two characters held things in that he liked. That's all we really discussed."

In Madden's remake of the 2007 Israeli thriller Ha-Hov, Worthington plays one of three naïve Mossad agents (the others are Jessica Chastain and Marton Csokas) dispatched in 1965 to East Berlin to kidnap a Nazi doctor responsible for some grisly atrocities and bring him to Israel to stand trial for war crimes; their mission goes hideously wrong and, 32 years later, Helen Mirren, Tom Wilkinson and Ciaran Hinds (Worthington's older self) are still dealing with the fallout of their younger selves' deception. "We know them from Munich where they're meant to be professional assassins, but in reality they were young, naïve, idealistic individuals whose driving force to be part of Mossad was something that had happened in their life," says Worthington. "David's entire family has been wiped out and he's trying to find some closure with that... I always saw him as a volcano and, when he erupts, it's about him trying to put the lava back in without getting burnt."

Before he achieved success as an actor, Worthington was a bricklayer down under – and his salt-of-the-earth background is undoubtedly part of his appeal. Worthington admits he's not entirely at ease with the trappings of celebrity.

He grew up in Perth ("bush country" he calls it). A keen surfer, as a youth he wanted to be a sportsman, but stumbled into his profession when he auditioned for Australia's National Institute of Dramatic Art at the age of 19 to give "moral support" to the girlfriend he'd been trailing around the country. Worthington got in; she didn't – and their relationship ended a week later. "I'd never thought about acting and, in hindsight, that fearlessness was what the school enjoyed."

It's also what audiences have enjoyed, combined with what Madden calls "a hidden vulnerability and sensitivity". The latter qualities give him a thin skin, though – he's not one to brush off queries he doesn't like with bland diplomacy. He'd much rather confront you head on. "Latecomer? I'm 35, mate, I wouldn't call myself a latecomer," he scoffs. "I'm getting into the third chapter of my career."

Apart from The Debt and Last Night, his third career will include sequels to his two biggest box-office smashes, both in 3D, albeit with differing results. "I was in the one that got revered and the one that got hammered," he chuckles, adding defensively: "Clash got roasted, but it made half a billion dollars, mate. Prince of Persia didn't do that. You've got to stand pretty proud of that fact, regardless of how bad the 3D was."

Determined to rectify mistakes, Clash of the Titans 2 is shooting with 3D cameras under a new director (Battle: Los Angeles's Jonathan Liebesman) – and with new hairstyling for Perseus. "What can I say?" says Worthington. "Mistake number one was having a shaved head because people cry their arse off about that. So this time I'm gonna have ringlets. Ringlets, man, I'm telling you!.. No matter what I do, I'm going to get nailed."

As for the Avatar sequels, they're scheduled to start shooting early next year and will take him out of action for most of 2012 and early 2013. Worthington doesn't mind, calling James Cameron his "best friend" (the two regularly go diving together). "We're all coming back," says Worthington. "I know it'll be a year or two years of my life, but I can't think of a better man to spend that with than Jim. I dig him, I love him."

Worthington has had more offers than he can possibly fit in. He's just worked "back to back to back to back" on the Clash sequel, the cop thriller Texas Killing Fields, the suicide drama Man On A Ledge and the Australian surf movie, Drift.

"Well, I do get criticised for working too much. Your whole life is planned in this industry so when you get time off, you do absolutely nothing."

'The Debt' is released on 30 September