By Chris Lee
September 26, 2014 at 06:30 PM EDT

In The Two Faces of January—a sumptuous adaptation of Patricia Highsmith’s 1964 novel of the same name that opens Friday—Viggo Mortensen and Kirsten Dunst portray Chester and Colette MacFarland, a golden couple embarked on a whistle-stop tour of southern Europe’s most glittering capitals.

Exuding wealth, privilege, and a uniquely American post-war pluck, the immaculately turned-out jet-setters’ fortunes grind to an abrupt halt in Athens where they meet an American tour guide named Rydal (Oscar Isaac)—an expat grifter with a straw fedora and palpable lust for Colette.

An accidental murder sets the three on the run together through the islands of Greece and, later, Turkey. As the authorities begin to close in, their allegiance to one another grows increasingly strained and—as with the best movies in the film noir canon—no one turns out to be who they initially seemed. “It’s nice to play someone with secrets,” says Mortensen. “I’m playing a con man who’s also a jealous husband. He’s got a lot of hidden fears. It’s a real banquet for an actor.”

Speaking from Spain’s San Sebastian Film Festival earlier this week (where he was promoting Jauja, the period drama Mortensen stars and co-produced), the actor voiced high praise for Hossein Amini, screenwriter of such films as The Wings of the Dove and Drive, who makes his directorial debut with Two Faces of January.

EW: Let’s get this out of the way. There are certain similarities between The Two Faces of January and another movie adapted from a Patricia Highsmith novel—The Talented Mr. Ripley—but plenty of differences too.

Viggo Mortensen: It’s similar in the sense that both movies are about American tourists in the Mediterranean in the early ’60s behaving badly. But the difference being that this is more focused on the characters. And they don’t separate and go in different directions. They’re stuck together. The Talented Mr. Ripley is a beautiful movie to watch and there are some talented people in it and [Anthony] Minghella was a great director. This one feels like one of those film noir thrillers from the ’50s. It’s not a retro exercise. Not, “Look at what I’m doing as a director. I’m copying that shot and everything is a picture postcard.”

Props to Hossein Amini!

Yes, it’s even more amazing that a first-time director could accomplish all that. The period look of it is perfect: the clothes, the location, the way it’s photographed. Hoss’ way was more discrete, classier in a way, more subtle. It starts in a similar fashion [to Ripley]: you’re on a sunny hilltop, you’re at a recognizable monument, the Parthenon. It’s almost Gatsby-esque. The people have these beautiful clothes and these idealized lives. You wish you could be them. And then it starts to descend rapidly. You go down this crazy wormhole. It gets darker as you descend. And by the end, you go from the sunny hilltop and this happy life to this sad life in the gutter, in the rain on some nameless street in Istanbul.

The production took you to the Grand Bazaar in Istanbul, the ruins of Knossos in Crete and the Parthenon in Athens. You and Kirsten are wearing perfectly tailored clothing throughout. It looked like fun! Fair to say this must have been one of the more pleasurable movies to film that you’ve done?

Even reading the script, I thought, “This is the way they used to make movies.” It was one of those rare situations where the shoot was a lot of fun. It was beautiful where we were. It was exciting. We had this great dialogue and we laughed a lot shooting the movie. Then you watch the movie and it’s really great. That doesn’t always happen. I’ve been on shoots that were a lot of fun. But then you watch the movie and you go, “Yeah, it’s okay. But I’ll always remember the shoot.” This time, we had a great time and we made a great movie.

Meanwhile, there’s a level of dread that ratchets up between your characters throughout the film. On paper, your character Chester is so reprehensible. He’s lost his moral compass. Yet, I still found myself rooting for him.

That’s what happens in those old thrillers. For example, The Third Man. There’s something about the way the movie’s constructed where you want the bad guy to get away with it! That has a lot to do with Hoss—Hossein Amini. He helped us all find the human side of the characters, the vulnerable side. That was key to the story.

I saw a blooper reel from the movie that shows the rapport that you, Oscar and Kirsten had. Despite the heavy vibe onscreen, you guys kept cutting up during takes.

We laughed a lot. It’s healthy. It helps to not take yourself too seriously and to remain flexible toward the other actors.

Shooting such dramatic material, it seems like that would be hard.

If I have to do a really emotional scene, I try to isolate myself and focus. But there are other scenes where there’s kind of a chess match going on between the characters and it’s good to crack jokes and see what happens. Some actors never talk to anybody between takes and stay in character the whole time. That works for them. The best thing you can do is be flexible. There are a million ways to skin a cat. It helps you do your job better and helps others do their jobs better. A movie is only as good as the compromise a group of people makes.

I understand Kirsten was extremely prepared heading into this project. She wrote notes all over her script and brought a lot to her role.

When you compare her character in the Patricia Highsmith novel to what’s in the movie, it’s a whole different ballgame. Kirsten added a lot more depth. Highsmith’s female characters tend to be underwritten. They’re objects, really. And Kirsten added many more levels to it. You can sense that [her character is] aware of a lot more than she wants to admit. She’s turned a blind eye to her husband’s criminal side—his shady side—for a long time out of an affection for him. When the movie starts, she’s been trying to make the relationship work for a long time. But it’s getting harder and harder. He’s a crook! The only thing you can be sure of about my character is that he cares about her.