Marvel's Agent Carter type TV Show network ABC

Agent Carter is about to uncover a whole new chapter of our titular heroine’s life.

During Tuesday’s episode, viewers will discover that Steve Rogers (Chris Evans) was not Peggy’s (Hayley Atwell) first real love. In fact, our favorite SSR operative was previously engaged. “I initially thought that Captain America: The First Avenger was the beginning of Peggy’s story and The Winter Soldier was the end of Peggy’s story — the bookends of her life,” Atwell tells EW. “Of course, what we haven’t touched upon until we get to episode 4 is what made her, what created this character and where she gets her tenacity, her discipline, her purpose and what drives her. That very much stems from her personal experiences in childhood within her family.”

The fork in the road for Peggy, as Atwell puts it, was the “option to marry versus an option to train as a spy,” which certainly wasn’t the norm for a woman in that era. “I thought maybe Peggy’s always had it in her, maybe she’s always been this tomboy and she takes that road and gives up on love, but she actually comes across a great dilemma — to receive the love of a really good man and have the security of a good life, or she goes on this completely off-the-wall, very abstract road that offers her extreme adventure,” she says. “We know whatever path she takes will shape her destiny.”

In making the decision we know will ultimately land her in the SSR, Peggy finds guidance from a surprising place. “This dilemma that she’s faced with at a young age is essentially the way in to understanding the relationship that she has with her brother, which becomes so pivotal in her development as a human being and as an adult,” Atwell says. “It’s her brother that sees who Peggy really truly is and what she believes will really make her happy, which is very different from what Peggy thinks at the time and what is probably the social norm for Peggy. It’s her relationship with her brother that really informs who she becomes. It’s very moving.

“A lot of who Peggy is as a character often comes from loss and grief and sadness, and there’s deep, deep wound there, but that’s where her heart lies, and also where her purpose, drive, values and her meaning lies,” Atwell says. “She’s able to use that pain in a very beautiful and transcendental way, which fuels her for everything that she goes on to do for the rest of the season.”

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The hour also draws a parallel between Peggy’s and Whitney Frost’s (Wynn Everett) childhoods. “It’s very much a nature versus nurture argument,” Atwell says. “On the one hand, you have Whitney Frost, who was born a genius — which does not come from any intellectual background or education, she’s just born with a brilliant mind not inherited from her parents. She grows up in an environment where she’s taught that she’s worthless. In her absolute desperation for power and a platform to be seen, she thinks Hollywood and being a famous actress will do it. Essentially there’s a huge hole in Whitney. She’s a broken person. She’s brought up in a neglectful and abusive environment. Because she gets fame and fortune, that deep wound manifests itself in a very destructive and negative way.

“Peggy is the opposite of that,” Atwell continues. “Peggy comes from an incredible environment of people with great dignity and integrity. It instilled within her a very strong moral compass. She was probably born with that as well. It was instilled in her that she was just as good as the boys. Instead of trying to iron her out and turn her into a lady, [her family] knows that’s what’s makes her happy, because that’s the essence of who she is, so they support that. You have someone who is broken and someone who is whole, and that informs the choices they make in life.”

Marvel’s Agent Carter airs Tuesdays at 9 p.m. ET on ABC.