Cormac McCarthy described the story as being about a man who makes a really bad decision. What can you say about your character?

I think the problem with the Counsellor is that he thinks he is smarter than he is. There's an arrogance to him that is going to be costly to him. I wanted him to be an everyday guy. I wanted him to be you or me, and he has simply over-pitched himself. He’s taken a risk and, without fully taking on board what the consequences of that risk could be, he finds himself out of his depth. He's given plenty of opportunities to pull himself out.

We find you at Javier Bardem's character's villa, at a glamorous pool party. Does he fall in love with the promise of the money?

Yes, and you look at the lifestyle of these guys and you realize that Reiner is spending his money because jail or death is imminent. You’re working with too many people that know your business. The crew you work with could do you in, the rival crew you’re working against could do you in, and the police could do you in. It's a constant state of paranoia and these people have to sacrifice a lot to stay in that world.

This is Cormac McCarthy’s first feature script; what's it like to chew over his dialogue?

Actually, I'm sort-of listening for a lot of it. The Counsellor, the character, is pretty sparse with his dialogue. He seems to be getting counselled by everyone else around him and yet he's the one called the Counsellor, so that's pretty interesting. The writing is so exquisite and sophisticated and you just don't get that opportunity very much. This is one script where you don't know what will happen next and how these characters are going to progress or regress. It's done so well by the amount of information that Cormac releases, and the amount he holds back or leaves open for either the actor or the audience to fill in the blanks. And that's a really fine balancing act.

There are these incredibly meaty exchanges in the script.

Yes, I always like to do long takes, because it's a lot of fun and there's more at stake for everybody, the entire crew. I think an energy is created and it's palpable. A nine-page scene with Brad Pitt, Ridley drops down to using just three cameras, and off he goes. It's brutal and beautiful. And for my character, there's this relationship with Penelope Cruz's character, which is quite real. Some of the things they say to each other could be seen as quite vulgar if it weren't two people in love and being honest with one another. There’s an honesty about their exchanges.

How much is Cormac a reference on set?

I don't ask him anything. My contact on set is the director. For me, the writer writes the piece and the director takes it and does with it what they choose. For specifics it's good to have him there, but I think I've only asked Cormac one question and it was about Malkina [played by Cameron Diaz]. There are blanks in the script and I don't even know if Cormac knows what's in them. I think he knows it's interesting to keep things blank and hint towards things but not spoon-feed anyone. That's what makes it so interesting… Everything's so transparent and predictable and he just crushes all of those things.

How does this differ to your experience with Ridley on Prometheus?

Well, we're moving faster. And Ridley would have preferred to move a lot faster on Prometheus too, but when you're dealing with 3D imagery and all that set-up time, it's time-costly. We're moving so fast on this and there's a fluidity too it; a flow. I had the privilege to work with this same crew on Prometheus, because Ridley is loyal, and obviously the team works like a well-oiled machine. It's great to be back and to see those faces, and not only are they top-notch at what they do but they're also very nice people, so it's easy. When you have a crew as big as Ridley's, with three or four different camera teams alone, and they all operate in tandem, it's pretty cool to see.

Does it help on day one, to have had a history with Ridley?

Definitely. I mean, I'm always nervous starting any job and week one is always when the character walks and talks for the first time in front of an audience, so I always get jitterbugs then. With Prometheus I definitely thought, "Oh my God, what is this going to be like?|" But Ridley and I got on immediately and the first thing that surprised me was how actor-friendly he is. He's very specific with actors and his notes are imaginative and practical. It's an absolute joy to work with him. And watching him work is special because he's got control of each department’s language and he can speak with them in their language and inspire them. It's pretty amazing to watch. He's always aware of everything that's happening on set. He had four cameras running today, plus the crane camera.

How do you keep track of where they all are?

It doesn't really matter for the most part. You always have an idea where they are so you can dress it up towards the camera.

You don't share any scenes with Malkina, played by Cameron Diaz. But how important is she to the story?

I don't have a scene with her, no. She leaves a scene as I enter – we brush shoulders and I'm aware of her because I know Reiner. We filmed it today. She's very comfortable in Reiner's world, while he only thinks he is, but he's just as out of his depth as the Counsellor. It’s a fantastic cast of people this, and a real mix. It's been great to play opposite Brad Pitt. We've done quite a few things together now. We were in Inglourious Basterds together, but we didn't have that much, but this year I've worked with him a lot, in this and 12 Years a Slave. I feel quite privileged to be in this position. It's one thing to get work, but this kind of opportunity really far exceeds expectations.