Prometheus star Noomi Rapace is set to get her Orphan Black moment in the upcoming Netflix thriller What Happened to Monday, with the actress taking on seven roles in an undertaking she describes as “the hardest thing I could ever imagine.” Rapace, who is next set to appear in the action flick Unlocked, talked about the challenges of filming the sci-fi movie in a recent interview with Looper, explaining why she stuck with the “unique” script despite a grueling shoot. In What Happened to Monday, Rapace plays seven sisters living in a future where families are limited to having just one child. In an effort to keep the sisters a secret, their grandfather (Willem Dafoe) names them each after the day of the week and says they are only allowed out on that day, all acting under the shared identity of Karen Settman. When one of the sisters goes missing, though, the others must come together to find her.

What Happened to Monday garnered a lot of buzz with its first trailer, which racked up over 500,000 views on Netflix’s YouTube page in just a few days after its release. Based on Rapace’s comments, the buzz seems to be warranted, with the actress saying that she was drawn to sign on to the movie because the story is “so unique.” “I hadn’t seen it before,” she said, adding that it was initially set to be about seven brothers before she came on board. “It was just completely different from everything I’ve ever seen.” However, the movie’s distinct storyline presented many difficulties, with Rapace having to figure out how to get into the heads of seven different characters, all of whom have their own distinct personalities and looks. “They were very close to me, all seven of them,” Rapace said of her characters. “Even though they’re very, very different, it was almost like a different part of me.”

The actress said that she used music and perfumes to help her get in the right mindset when she was becoming each of the distinct characters. “I used different kinds of tools to help myself reset and clean my head and kind of clear out and then step into a new one,” she said. “But it was extremely hard. I’ve never worked so hard in my entire life.” Shooting took nearly five months, with Rapace called to set almost every day. Most of the time, she was acting by herself, using a green screen with tennis balls or crosses and listening to her own pre-recorded dialogue in an earpiece. Sometimes, they used doubles, with Rapace showing them exactly how she had acted out the scene when she had been the other character. “Let’s say I’m doing a scene with Saturday and I’m Monday, and then I have to kind of plan what I’m gonna do as Saturday before I’ve done it and then I have to show the double girl how to move, and how to sit, and what line she will reach for the glass, because if we already established it with her I need to fix it later on when I was playing Saturday,” she explained.

Still, despite the tough shoot, Rapace says she was proud of the project. “I love a challenge, and this was the hardest thing I could ever imagine,” she said, adding that she could feel a connection with her characters because they were all, like many of her past roles, “women fighting in a man’s world.” Hansel and Gretel: Witch Hunters’ Tommy Wirkola takes on directorial duties for What Happened to Monday, working off a script from Max Botkin (Opposite Day) and Kerry Williamson (Alex Cross). The movie, which also stars Glenn Close, is set to hit Netflix on Aug. 18.