In “The Secrets We Keep,” Noomi Rapace’s Maja harbors a dark secret, one she keeps to herself. She plays Maja, a Romanian refugee during World War II, who has set up a new life for herself with her husband Lewis, played by Chris Messina.

She’s settled into her life, but one day, her past and the secrets come back to haunt her in the form of Joel Kinnaman, who plays Thomas. Is he really the SS officer who she holds responsible for her younger sister’s death? He denies it when she confronts him.

For costumer Christina Flannery, her goal on the post-World War II drama was simple — to be as authentic to the period as possible. As a former vintage store owner, Flannery looked at the detail of the period from the stitching to the buttons to dress her characters.

Below, Flannery talks with Variety about putting the look of Bleecker Street’s new release together. “The Secrets We Keep” is available on demand starting Oct. 16.

What was your initial approach to the costumes, especially when it came to research and accuracy?

It was important to do things as accurately as possible. I grew up in the vintage world and I owned a vintage store in New Orleans, so it was kismet for me.

I did a lot of research looking into what buttons, what colors, and what patterns to use. I watched a lot of documentaries and worked closely with director Yuval Adler and Noomi on the looks, especially with her character Maja Stowe.

The hardest part to do accurately was the Romanian Nazis. You couldn’t see the subtle tones and the additional work that goes into the detail, but it was so important to do your research and to be accurate, and not let the clothes overtake the actors or a scene.

How did you want to introduce Joel Kinnaman as Karl/Thomas and who he was?

He’s this working-class person trying to blend in. He had this period-appropriate look, taking his clothing down to look like he worked in this factory, and he was just filthy [that was a hint to who he was]. The key to him was to keep it simple and basic because he really needed to blend in. You didn’t want the viewer to know if he was this person that Maja was accusing him of being or if he wasn’t.

For his color palette, we put denim on denim and used muted colors. We used blues and kept him in a basic color palette; creams, light grays and things that blended him into the environment.

What went into the idea behind Maja and her styling sensibility?

Noomi is such a powerful and amazing person. I wanted to build this rich jewel tone with her clothing. She has this influence of Romanian culture. Almost everything of hers was built.

She’s wearing a dress later in the film with is made with green and has this flowing A-line so she can jump and bounce all over the place, and keeps the flow of the ‘50s fashion and style.

There’s a scene where she’s with her son later wearing a red two-piece set. What I loved about Noomi is that she said she was drawn to revenge stories, and it’s so great to show this character who is a badass, not taking crap, and we don’t see that so much.

We were able to take this woman who is completely in control and losing her s–t. But we had to show her vulnerability, so I put her in a white nightdress on her when she’s on the porch, and that was almost virginal where you look at her and you want to help her.

What about Chris Messina’s wardrobe as Lewis — he’s this rich, well-to-do character?

I loved his wardrobe. I wanted to create this like a realistic world that anybody could find themselves in. He has suspenders and was working as a doctor in this small town. He’s just getting going. I put beautiful colors on him and made him authentic to his world, trying to blend him in.

I’d go on Etsy and see things I liked and put things together. We worked in New Orleans, and I was fortunate enough that I had owned the store there and could also reach out to people I knew to help.