“Maria Full of Grace” writer and director Joshua Marston continues to explore the concept of identity with his latest film “Complete Unknown.” The film, distributed by Amazon, stars Rachel Weisz and Michael Shannon, in a crossing of paths that threaten to wreck the stability in Shannon’s life. Variety spoke with Marston about working with Amazon for his newest film and why a female lead provides a more intriguing vantage point for storytelling.

Where did the idea come from for “Complete Unknown” and how did the concept of identity become the focal point of the story? 

It started from the idea of wanting to write a character who is not who she presents herself as being. Also my own personal fascination with the idea or fantasy of pulling off fakes, moving on, wiping the slate clean and starting completely over. And wondering what it would be like to actually do that and the wondering if you change completely what happens if after a while your new identity starts to run thin or starts to get old, do you stick with it? Do you go back to who you used to be or do you change again and become a third person? What happens if once you’ve done it a fourth and fifth time you’ve gone so far and deep in there’s no turning back?

What was your personal fascination with that concept?

I think, for a lot of people, you get in your car in the morning, back out of your driveway and go to work and do it day after day after day and wonder what it would be like to make a change and maybe just keep driving. I think that’s a fantasy that a lot of people can relate to and something that I wanted to explore.

Was there a reason you made your main character a woman?

She was a woman because she was a woman, we didn’t really think about it. Then we gave an early draft around to readers and we realized that men and women responded to it differently. It was tricky to make sure people had sympathy for this character. There is a certain amount of manipulation going on, leaving people in her wake. It was really important to understand on a deeper psychological level what was going on with her but to make her also vulnerable, so that was a challenge.

In the process of thinking that we also explored what it would be like if we changed the gender of our character and made her a man. Would that change the expectation? Are people concerned about her being unsympathetic because she’s a woman doing this? The reason why she’s a woman is because men do what she does all the time at a certain level. For millennia, men in patriarchal societies at the very least have left home and gone out and gathered while the woman stayed home. In more modern times, men leave their families behind, and some become deadbeats and move on to another life. So the idea of a man doing it is not new and not as interesting. The idea of a woman who patriarchal, misogynistic, sexist, [and] society tells us is supposed to stay home and take care of the kids is instead getting up and leaving everything behind. That’s a really challenging idea so that made it really interesting for us and it was something we wanted to explore. Why wouldn’t a woman do this? Why should it be more questionable for a woman to do than for a man?

Why were Rachel Weisz and Michael Shannon right for your leads?

We decided that rather than waiting until deep into the process, I wanted us to collaborate early on with the actress that was going to play the part. I’ve long been a fan of Rachel Weisz, the camera loves her and she conveys a mystery, an intrigue and a depth when she’s on screen and those are all things that I needed for this character that is so enigmatic. I literally sent the script to her on a Wednesday before Thanksgiving and on Monday heard back from her, that she read it and wanted to meet.

We had a great first meeting where we dug into the questions of identity and what the character does and who she is and why she does what she does. And then we started the relationship of writing, talking and rewriting.

As for Michael Shannon, I was really interested in the idea with seeing someone who is normally associated with playing a psycho-killer and a terrifying menace playing an ordinary guy going through a midlife crisis. I think he does it magnificently and with a real level of depth and humor that the script requires. We had a screening last night and when you watch it with an audience you really become aware of how many laughs he gets. It’s quite a funny performance.

How is “Complete Unknown” different from your previous films?

It’s in English and it’s with movie stars, for one. That’s certainly an enjoyable change of pace and it’s not a research based movie. My other movies relied on certain level of almost journalistic anthropologic research. This is more imagination and pure writing. All three movies still have something in common, I always have an interest in identity and in characters who are trying to define themselves and the world around them.

How did the partnership with Amazon happen?

Amazon came into the picture just as we were going to Sundance. We screened it for them and decided we would seek distribution before we got into the hurly-burly of Sundance. Which Sundance is great and I have a long relationship with them. They screened “Maria Full of Grace” and I have since become an adviser at the Sundance Lab. We have a wonderful time screening films there.

But the business side of things at Sundance can be a bit overwhelming and often obsessed with making that new discovery to the exclusion of seeing everything that’s on the landscape. Rather than trying to compete with the craziness at Sundance we decided to find a distributor ahead of time.

What was your biggest challenge as a director in the film?

I think the challenge was shooting a movie that was originally conceived as a small contained film that was shootable on a low-budget so that the film wouldn’t fall apart. My previous film had fallen apart before this so we didn’t want to run the same course. And then once we got into “Complete Unknown,” I realized I had written a character who has an immense scope, a woman who has crossed the globe living multiple lives in countries all around the world. In order to really understand the character you want to feel the breadth of what she’s done. We had to be very creative in conveying that and making it look like as big of a movie as possible on the small budget that we had.