''There are really nice trajectories between his life and mine,'' says Chris Evans, deflated to human size to promote his third full outing as the star-spangled superhero in Captain America: The Winter Soldier.

''He's a celebrity, he is. Everyone knows his face; everyone knows who Steve Rogers is. That type of exposure might not be exactly what he's looking for. His conflict with who he's working for right now, with SHIELD, [raises] questions of what he wants and what is the goal - how to achieve happiness.

''You do things that you feel are your responsibility; you're given an opportunity to do something. But, at a certain point, it may not bring you the happiness - peace - you want, and it makes you question why you do these things.''

Popular misconceptions of Captain America as jingoistic, fighting flag aside, he is actually one of the more thoughtful Avengers. He resisted the government's ''Superhuman Registration Act'' in the comics' famous ''Civil War'' arc (a thinly veiled security-v-freedom metaphor). In a '70s, Watergate-inspired storyline, when he saw corruption run all the way to the top, he even renounced his colours and briefly became ''Nomad''.

So, yes, Captain America: The Winter Soldier has the most action and best combat of any Marvel movie thus far and, yes, it retains the humour that has kept the other entries buoyant. But it is also the studio's most grown-up effort.

''Even if we took the superhero element out, I still think it would be a good movie,'' says Evans. ''I think the plot could still captivate an audience. I don't fly, I don't shoot missiles, I don't call down lightning. They really leaned on plot and how things work from a character standpoint.''

That might sound like junket-speak, but, in this case, it's true. The Winter Soldier features expertly executed action sequences with Black Widow (Scarlett Johansson), Nick Fury (Samuel L. Jackson) and the newly introduced Falcon (Anthony Mackie), Cap's sidekick in the '70s comics. But more to the point, Cap uncovers a massive conspiracy that rattles the foundations of his mission.

Towards that end, the series shifted its tone from the rah-rah, '40s-style propaganda of Captain America: The First Avenger to the paranoid political thrillers of the '70s, such as Three Days of the Condor. Robert Redford is even on hand as a high official who knows SHIELD's dirty secrets. To get there, Marvel took a typically unusual path, choosing Joe and Anthony Russo of two of television's smartest sitcoms, Arrested Development and Community, to direct.

''When I first heard their names, I'd be lying if I said I thought they were the perfect fit for the job,'' Evans says. ''When I read their resume, I didn't see many parallels, but that goes to show you can't trust the resume. This is why [president of production and Grand Pooh-Bah of the Marvel Universe] Kevin Feige is a special man; because he's able to see people for their potential and not for their past.''

The Russos' film takes a matter-of-fact tone, despite moments of humour, and even sometimes uses hand-held cinematography to create a more immersive, immediate feeling. One thing directors and star agreed on was updating Cap's combat style.

''In the first couple of movies, it's very meat and potatoes: punch, punch, kick, kick. But this guy can't just be a human who can fight. We need to see the superhero element. We need to know why he's earned a spot on the Avengers team.

''I brought up the Captain America video game; his fight style is so acrobatic, there's this aerial fluidity to everything he does. 'Why doesn't Cap move like this?' '' Evans flashes a huge smile.

The film generates moments of earned emotion, especially in a brief flashback to Rogers' pre-war days and a present-day visit with a character from the first film.

Evans agrees that building on the stories already told is a major advantage. ''You don't have to wrap up your entire story in two hours because in about six months we're gonna have another instalment.''

But the character's thoughtfulness is what makes the role so meaty to Evans. The dogma-averse actor reluctantly calls himself a Buddhist, he says, ''to start a conversation''.

''It's just a label. It's just a way of being,'' he says. ''It's about being present, being able to drop into the moment, recognising the noise your brain makes is not who you are; that is brain noise. If you can drop into the now, you win, because that's all you ever have, is right now. You'll never meet the future. When the future happens, it's now. Life is a series of nows,'' Evans says.

Acknowledging that the real engine that drives Steve Rogers is not the super-soldier serum but his unwavering moral fibre, Evans says: ''When you have somebody who refuses to bleed on people, it's hard to make his story complex, because he's gonna put himself last.

''There's a great line [in Kahlil Gibran's On Pain, he paraphrases), 'Pain is the breaking of your shell of understanding.' I'd love to see Cap feel something he thought was right be wrong. I'd love him to be confronted with the fact that even the things he believed in so completely can still be a question mark.'' AP