“Mother,” Spanish director Rodrigo Sorogoyen’s anticipated feature follow-up to the 2017 Oscar-nominated short of the same name, premieres in Venice Film Festival’s Horizons sidebar on Friday.

While the feature shares the short’s title and main character, played with great intensity by Marta Nieto once again, the narrative will catch Sorogoyen and regular co-writer Isabel Peña’s fans a bit off guard. Best known for their work on thrilling fare “The Realm,” which received seven Goya nominations from the Spanish Academy, or their 2013 breakout feature “Stockholm,” the two have forgone the predictable thriller follow-up in favor of a more personal drama about a woman’s recovery from unthinkable trauma.

“Mother,” the feature, starts with the 19-minute short acting as a prologue: Elena receives a call from her son, six-years-old Ivan, saying that he is lost on a beach in France and can’t find his father. The film picks up, a decade later, on the same beach where her son disappeared. A now-graying, gaunt Elena wanders the beaches of France’s coast between shifts at a beach-side bar.

On one of her walks, Elena crosses paths with a boy, about 16 with red-ish hair like Ivan’s, and begins following him. Eventually, the 39-year-old woman and teenage boy embark on a relationship which at first elicits sidelong glances from friends and family before spiraling out of control.

Sorogoyen talked with Variety ahead of the film’s Venice premiere.

Your short was an instant classic thriller, but for the feature adaptation you’ve gone in another direction. Was that always your intention?

Before I even started shooting the short, I had the idea it could be a feature. I’ve also always imagined it as something very different than a thriller. Isabel and I could have done something dark, a psychological thriller, but for me the film was always about a mother, years after she’s lost her son, and her encounter with a child that reminds her of the boy. After our last few features, we were both a bit tired of these big thriller films. It’s a genre that we both love but we don’t necessarily consider ourselves specialists in or limited to. For both of us we needed a change, and to make a smaller, more intimate movie.

Can you talk about Isabel and her importance to your work? Your name is always first as the director, but she seems equally as vital to the work you do.

Totally! Isabel and I are an inseparable team. She provides our work with something I don’t have, and I like to think she’s delighted with me as a director when she sees our words come to life on the screen. We love the process of working together and a lot of fun. We stay in very close contact when we are developing a story.

Now we see where Ivan was when he made that horrifying call. How did you settle on this location in France?

When I wrote the short, one of the few things I’ve ever written without Isabel, I just imagined any place outside of Spain where a father and son might go together, and for that I really liked the Landes region of France. It’s close, but foreign enough that the language barrier would make it much harder to find the boy. I studied French and did an Erasmus program in France and still have a lot of love for the country. When we were scouting sites, I remembered that I had summered in this area five years ago and I couldn’t imagine doing it anywhere else. There are big beautiful beaches that are bleak and scary in the winter, but in summer they are beautiful. I really liked that contrast.

You never say what happened to Ivan. Do you know? Or has that stayed a mystery even to you?

I don’t know why, but I never wanted to get into that. I don’t want to answer it for myself, and obviously not for the audience. I enjoy, and I think it’s something I do often with Isabel, putting myself in the skin of our protagonist. I find it frightening that Elena doesn’t know what happened. The drama in Elena’s story is not knowing what happened. This film isn’t about what happened to the child, but about how a person overcomes such a loss. To focus on what happened would take away so much of the film’s energy and I think it was the right decision not to tell the audience what happened.

As was the case in the short, Marta Nieto does a lot of the heavy lifting. Can you talk about working with this break-out actress?

Working with Marta, as with any actress at her level, is a challenge and a pleasure. She was completely open to doing what was needed for the role, whether that was learning French, losing 7 kilos or immersing herself in this tragic situation. Marta’s profile is growing in Spain, and I hope now the world will give her the recognition she deserves because I couldn’t imagine another actress in this role.