Actress Karen Gillan -- famous for action-comedy roles -- says she signed on to star in the new psychological thriller Sleeping Dogs because it allowed her to play a mystery woman in a story filled with secrets, lies and unreliable memories.

"When I learned more about who I would be playing, that's when it became a no-brainer. I get to exercise a little bit of the transformational aspect that I enjoy."

Co-starring Russell Crowe, Martin Csokas and Tommy Flanagan, the film is an adaptation of E.O. Chirovici's mystery novel The Book of Mirrors, which was adapted by Adam Cooper and Bill Collage and directed by Cooper. It premieres in theaters Friday.

The story centers around who killed a popular man with a lot of secret enemies.

Gillan plays Laura/Elizabeth, a brilliant psychologist who was romantically involved with the victim, Dr. Wieder (Csokas), a college professor working on a new drug that might help traumatized people forget painful memories. Flanagan plays Jimmy, Roy's former partner.

"She is a very interesting character. She wears many masks. She adopts a few different personalities, depending on the situation that she's in. She is a psychology student, so she is incredibly clever," Gillan said of her character.

Gillan, who said she is a huge fan of suspense movies like Silence of the Lambs and Shining, found Laura/Elizabeth to be a fascinating character and did a lot of research into what might make someone like her tick.

In addition to speaking five languages, Laura/Elizabeth also has degrees in math, psychology and art history.

"The main thing I did was try to figure out who she is as a person and why she is so performative. Then I did a deep dive into what type of person does wear masks in their life and what type of person or disorder is manifested in adopting different personalities," Gillan said.

"I also decided she was the type of person who might study people that she deems to be intellectuals and she watched their videos on YouTube even and adopted their mannerisms," she added. "So I watched a lot of Cate Blanchett in Tar and then [author and psychologist] Jordan Peterson."

Although Gillan and Crowe appeared in the 2022 Marvel blockbuster, Thor: Love and Thunder, they didn't share any scenes together.

"It was so cool to work with Russell," she said. "He is such a brilliantly skilled actor and he knows all about the cameras and the lenses and the technical side of it, but then is so present, emotionally. Just watching him, I'm like, 'That's why you are who you are because you have the thing.'"

The Scottish actress noted that although everyone in the cast was playing American characters, most of them were from the United Kingdom or Australia, where the movie was made.

"There were hardly any Americans playing Americans in this film. Even our dialect coach was from England, teaching us how to sound American," she said.

Since she wasn't in every scene, and there were so many twists and red herrings, Gillan actually was able to watch the movie and enjoy the suspense as a viewer.

"It evolved from the first script that I read in a really interesting way, so I got to watch it with fresh eyes, in a way," she said. "When I was making it, I was more in it and focused on my character than seeing how the whole puzzle fit together."

When it comes to choosing her roles, Gillan doesn't have a scientific strategy.

"I probably should," she said with a laugh.

"A good sign is when I read the script and start saying the lines out loud because it's just fun. That's happened to me a few times, and that is a surefire sign that I'm going to want to do this," Gillan added, explaining that she considers the filmmaker, script, her character and people behind the scenes before she accepts a role.

"I can try to have some sort of strategy, but I think it's just a gut instinct," she said.