Michelle Monaghan Says Playing Identical Twins in Netflix's 'Echoes' Was 'Incredibly Challenging'

Michelle Monaghan is always up to push her limits as an performer — and portraying life-swapping identical twins Leni and Gina in the Netflix thriller Echoes was just what the actress needed

"It was incredibly challenging," Monaghan, 46, tells PEOPLE. "The prep for both of the characters is really an intense period of really trying to individualize two very different distinct characters and characters that I could drop into very easily back and forth. And so it was creating characters that felt very unique, with very different energies and body languages and accents and physical looks."

She explains that "the more technical aspect of that was shooting a very long scene where I play one character and then going and changing into the other character and shooting the other side."

"And so we would do that multiple times a day," says Monahan, "and that became very intense. However, I was very laser-focused. But the dialogue was difficult to keep up with, learning all the lines, of course."

The limited series kicks off with Leni's puzzling disappearance, which leaves Gina to pick up the pieces all while attempting to maintain their secret.

"The show is really a very kind of pulpy mystery thriller," Monaghan shares. "It's seven episodes, very binge-worthy."

Of the sisters' "big secret," Monahan goes into more detail: "Ever since they were children they used to switch identities and fool everyone flawlessly. And it culminates and escalates even into adulthood. There's some things that happen that they choose to start switching identities once again later in life. So they live two lives, two homes, live in two different cities. They share husbands, they share a child and everything gets thrown. It's perfectly choreographed and everything gets thrown into disarray once one of the sisters goes missing."

For Monaghan, who is best known for her roles in films such as Made of Honor and Mission: Impossible III, taking on this particular role was a no-brainer a from the start.

"I was surprised and shocked and intrigued at what I kept reading and the cliffhanger after every episode that I went, 'Oh my God, this is for real,'" she said about first reading the script. "And then I thought, 'This would be such an acting challenge of a lifetime.' And it scared the living daylights out of me, to be honest. And yet I had to do it. It was so compelling to me."

"I was just so excited to get to play two different characters and see if I could really pull it off," she added.

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Echoes is streaming now on Netflix.