The eponymous prior evening of Massy Tadjedin’s Last Night takes the form of an out-of-town business trip between handsome, somewhat taciturn and very married Michael (Sam Worthington) and Laura, his sexy and very interested coworker (Eva Mendes). Or, you could view it, the “last night” is the clandestine evening spent between Sam’s beautiful author wife, Joanna (Keira Knightley) and her still-charming ex, Alex (Guillaume Canet), while Sam is away. But most accurately — and no matter what your gender or point-of-view on modern relationships is — the film’s “last night” is best considered from its morning after, when whatever rash decisions made hours before are confessed… or concealed.

With an ending that’s bound to instigate hours of date-night conversation among couples, Last Night is a skillful debut picture from screenwriter Tadjin (The Jacket) It’s the kind of serous relationship drama that isn’t made so much anymore, and it’s given shape and edge by its single-minded focus on the theme of infidelity in all of its forms. (For those who don’t follow its emotional subtext, Griffin Dunne helpfully appears mid-film to spell it out.) Knightley is enormously empathetic, bringing her star power to a layered portrayal of a woman at a crossroads she doesn’t know she’s at. An emotionally torn Worthington couldn’t be further away from Jake Scully, and both Canet and Mendes find original beats in their roles as possible paramours. In a partnership between Miramax and Tribeca, the film has been available on VOD and opens in limited theatrical May 6.

Filmmaker: So, what drew you to the theme of adultery and exploring it from different points of view?

Tadjedin: I don’t know what drew me to it. It’s not an autobiographical film — it’s not based on an event in my life — but it is a personal film. It’s certainly about issues that I think anyone who is in a long-term relationship thinks about. But also, it felt to me like a modern romance. When I wrote it, I thought, yes, [the characters] are grappling with the issue of fidelity and infidelity, but it certainly didn’t originate from a position of wanting to analyze these themes. I just went to the blank page and wrote a story. And this is how it came out. When I wrote it, I pictured it more as a romance story, or a suspense story. It wasn’t until I began to meet actors and crew that I realized how sharp the focus was on fidelity and infidelity.

Filmmaker: It struck me as very specific in the way it dealt with this subject because the ending literally propels people into the lobby talking about it. The ending is like a post-movie conversation starter.

Tadjedin: Good!

Filmmaker: But also, the movie seems to very consciously contemplate the different kinds of adultery — emotional and physical.

Tadjedin: I think the gray is the part of life I am most drawn to — I think that grey area is where most of us live. I wanted to portray these characters sympathetically and honestly and just sort of show how even people with the best of intentions can find themselves in these predicaments. I genuinely think at the beginning of the film, none of the four are aware of what is around the corner. I really wanted to show how these transgressions, these temptations, these choices, these predicaments, they happen in inches. They don’t happen from premeditated desire. It’s hopefully a more honest depiction of how people falter, or work their way through these situations.

Filmmaker: Is it fair to say that the movie posits that adultery can function in different ways and that emotional adultery can be as significant as physical adultery? Or that there’s a male/female split in terms of which kind of adultery is worse?

Tadjedin: That’s really interesting. In my experience making the film, there wasn’t an even male/female split in terms of the perspective. I do think that there are definitely two forms of infidelity. Maybe [I didn’t] at the beginning when I was writing it but by the end I was aware thatt we are depicting two different kinds of infidelity, the emotional and the physical. And I should say I wasn’t interested in weighing what was worse. To me that wasn’t a worthwhile way to spend an hour and a half, trying to measure whose behavior is worse than the others. But I did realize when we were filming that that judgement was going to come down from [viewers]. And it was over the course of filming that I began to listen to the crew, who were weighing in on which storyline was actually more damaging to the marriage. We shot Alex and Joanna’s story first because I wanted it to feel like a part of Joanna’s past that she experiences before her present time with her husband. Then we shot Laura and Michael, then we shot Joanna and Michael again. And it was so interesting — over the course of the shoot you had different assessments, judgments and indictments of what these people were doing. And it wasn’t evenly split among the men and women.

Filmmaker: What was the nationality of the crew? I know you had French financing.

Tadjedin: The crew was all American. The cast is international, but the crew was all American, and we shot in New York. The cast is international, but it wasn’t really by design. I didn’t simultaneously cast all four — you sort of have to build a cast like this to ensure they are a good fit. I began with Keira, so then the chemistry, for example, between Joanna and Alex had to be distinct from the chemistry between Joanna and Michael. You are presenting two different paths her life could have taken. The same with Laura. I wanted someone with a different physicality from Keira, but also Eva brought a certain warmth to the character that I thought would make “the other woman” more sympathetic. It’s sort of this piecemeal casting process that we ended up with a woman from England, an Australian man, a Cuban American and a Frenchman, but to me it felt really organic.

Filmmaker: How did the cast reinterpret your script, and what sort of observations on the topic did they bring?

Tadjedin: It was interesting, the cast was also sort of split, especially once they started to inhabit their characters. In our early conversations, they were each sort of split about whose behavior was a greater transgression in terms of fidelity. I think it was Keira who echoed what Peter Deming, our cinematographer, felt, which is that what Michael does may test the marriage but what Joanna does arguably could wreck it. It’s a different beast emotional infidelity. It’s often not consummated; it is a different circumstance than a sexual affair. With the emotional affair, you can imagine a life that is different from your own — the old “path not taken.” There’s the idea that there is someone left behind at one point or another. Emotional infidelity can be a kind of engagement with that possibility, and it’s dangerous to the circumstances of real life because you are imagining [those circumstances] changing. A physical infidelity, I’m not sure that is as radical a departure from the circumstances of real life. It may be more of a “time out” from real life.

Filmmaker: Did the actors have personal feelings towards the material?

Tadjedin: I think everyone’s personal experience came into it. I met Sam Worthington while he was filming Avatar. I had seen him in this Australian film called Plummer’s Salt. He said very candidly that he had been all of these four [characters] at one point or another. A lot of us have been one or more of them at one point or another. Which is part of why there have been so many films about this, you know? We sort of haven’t figured it out yet… and I don’t think people ever will.

Filmmaker: This is your first feature — how did you come to make it?

Tadjedin: I wrote it about four-and a half years ago, but I had been writing before that. I studied English literature in college, and I knew I wanted to direct since I was probably around 12. After college I got a job as an assistant to a literary agent. I read screenplays to learn how to write them, and then I began writing. My first break, really, came when I wrote The Jacket for Section 8, which is a company that George Clooney and Stephen Soderbergh had at the time. They gave a lot of writers and directors a break. After that I started getting screenplay work, and that led me to meeting producers like Nick Wechsler, who was the producer of Last Night.

Filmmaker: And Keira Knightly is in The Jacket as well.

Tadjedin: Yes. I became friends with her on the set of The Jacket.

Filmmaker: I think a lot of people think that writers maybe aren’t present on sets or that have very little contact with the filmmaking apparatus, but for you this obviously wasn’t the case.

Tadjedin: No, that wasn’t the case for me. I was on set, for not the whole film but a good portion of it. Keira and I met there, and we really hit it off. We stayed in touch and became close. That was great because it’s hard on your first film to persuade people to take a chance on you. Keira was great because she sort of anchored the cast once we got her to come on board. She didn’t want to work originally for a year-and-a-half when I sent the script to her so I really had to persuade her — I had to keep talking with her until she just relented and did the film. (laughs)

Filmmaker: Were there things about her and her acting choices you learned on The Jacket that played into how you decided to direct her on this film?

Tadjedin: It’s great when you do know an actor, when you have a history with them. There’s an immediate intimacy that makes the work much more comfortable from the start. I mean, filming by nature is an awkward process when you have a low budget and a very finite amount of time. You often are going to a very emotional place in a very short amount of time, and you are working, often, with actors you haven’t worked with before. When you actually have history with someone it does make a difference, I think. You know their mannerisms, you know when they are comfortable, you know when they are looking natural in a scene, you know when something doesn’t feel natural and therefore maybe won’t be natural in the performance. You know their inflections and you know how angry they can get. You know their qualities, and that informs the performances. It’s often those qualities that you cast them for, those qualities you want them to embrace. For me, knowing Keira and working with her as Joanna, was very natural,. It felt really comfortable. I felt that same way about our cinematographer — he shot The Jacket for us, and it was enormously comfortable that every time we cut I could look behind the camera and see Peter’s face.

Filmmaker: What about Sam Worthington? You cast him before all the Avatar success, right?

Tadjedin: I met him while he was filming Avatar. Obviously it was James Cameron so nobody thought it would be anything less than something large, but we didn’t know at the time what it was about or anything. I connected with him instantly. I think he’s very sympathetic in the role of Michael because he didn’t try to map out what Michael was going to do. He really let Michael react to what was happening. Then at the end he brought this sort of unexpected awareness that Michael did know what he was doing the whole time.

Filmmaker: How about the other two cast members?

Tadjedin: Guillaume Canet I met as a director. He was in L.A. screening his film Tell No One. I saw him at that screening, and he made a very deep impression. I thought he would have a great and different chemistry with Keira and Sam, so I cast him. Eva I knew immediately I wanted to work with because she is very warm and generous. I think she brings a lot of sympathy to the role. I feel like she’s really humanized Laura in the respect that this woman is flawed. She’s not looking to break up this marriage, but then at the end I think her own expectations are a little subverted. Sometimes people [like her] are just living in the moment. They’re not thinking about “your marriage” or “your relationship.” I think her character is really interesting because in a weird way she’s the most moral. Or the most honest, I should say. The most forthcoming. She always lays out what she thinks. She’s very clear about the fact that she believes life is a succession of moments, and you steal them when you can because there aren’t that many, and you make the most of them. I feel like there’s a black and white-ness to her morality and that even though she is the temptress, even though she is the other woman, it’s really noble. Whereas these other characters are very human but they think that they have higher ideals about their behavior [than they do]. I think she has a very healthy and honest approach. You know?

Filmmaker: Were there other dramas or stories about couples that inspired you in any way?

Tadjedin: Oh my goodness there are so many. I love Brief Encounter, the David Lean film. I love Bergman’s Scenes from a Marriage. I love Husbands and Wives, I love Carnal Knowledge. I love Mike Nichols’ Heartburn. I love sex lies and videotape. I think I’ve been drawn to a lot of these films over time because these stories just come close enough to your own home or your neighborhood to make you uncomfortable and to engage you. I think that I’m drawn to that body of work.