Elizabeth Mitchell Explains The Motivation Behind Her FBI: International Character - Exclusive

Even though she's only a guest star, Elizabeth Mitchell's presence looms large over "FBI: International," and she'll be returning to the show for the Season 1 finale, which airs tonight on CBS.

As Angela Cassidy, Mitchell portrays the estranged mother of FBI special agent and Fly Team leader Scott Forrester (Luke Kleintank). She worked for the U.S. government before allegedly selling information to the Russians, abandoning her son when he was just a teenager. Now, 15 years later, she has re-emerged in his life seemingly in hopes of getting a second chance and clearing her name. But the big question is: Are those her true intentions?

For Mitchell, who's probably best known as Dr. Juliet Burke on the hit series "Lost," joining "FBI: International" as a pop-in character was a "no-brainer." But just how does she wrap her head around playing a woman who cast aside her son to betray her country? It's a question that Mitchell answered when she recently sat down for an exclusive interview with Looper.

As a mother herself, Elizabeth Mitchell admits that she found it difficult to play a woman who abandons her son on "FBI: International" — but she believes Angela Cassidy has a good reason. "I really struggled with that a lot, and the only thing I could think was ... instead of saying 'I would never,' I say 'What would make me? What would make me abandon my son?'" says Mitchell. "There's really only one thing: If I thought his life would be in danger if I were near him. That's the tact that I took ... and as soon as I made that realization, it flowed for me."

In real life, Mitchell's own son is around the age Scott Forrester would have been when Angela deserted him, but the former "Lost" actor doesn't necessarily see any part of herself in the character she's playing.

"It's heartbreaking, and that's probably what led to such a deep emotion [as Angela]," says Mitchell. "She's been doing this for a very long time, and she's very good at having people see what she wants them to see. That part of it was the most intriguing to me, because I don't cultivate myself in the same way. I am here, and I say whatever comes into my head. For her, it's more methodical than that."

But while Mitchell can't give away what's really going on with her "FBI: International" character, as an actor, she had to find straws to grasp at to make an emotional connection with Angela.

"A mother leaving their child is something that is really hard to wrap your head around," she says. "It's something we can't [understand] as a society, and even as a mom, you're like, 'How?' That's the only thing I can think of ... that by removing yourself from the equation, you save your child's life. Then it makes sense to me ... [As an actor], we have to choose things that feel true to us so that we can play in these imaginary circumstances as complete reality, complete truth. I did find it to be a struggle."

Tune in tonight for the "FBI: International" Season 1 finale at 9 p.m. ET on CBS.