The Underground Railroad stars Thuso Mbedu and Aaron Pierre on how the series changed them

Much to the surprise of director Barry Jenkins, actress Thuso Mbedu had not read Colson Whitehead's The Underground Railroad before she had a callback audition with the series creator for the lead role of Cora.

As she recalls, Jenkins asked, "How did you come up with the choices that you made for the character?" Mbedu responded, "I made choices from what I saw in the script." As the South African newcomer tells EW, Jenkins "couldn't wrap his head around that."

"I was grateful I was able to offer what I could prior to reading the book because I guess it built his confidence in me," Mbedu concludes. After securing the part, she finally dove into Whitehead's Pulitzer Prize-winning novel that Jenkins would adapt into a limited historical drama for Amazon Prime, and, she says, was able to take the performance to another level.

Mbedu describes Cora, who is an enslaved young woman on the Randall plantation in antebellum Georgia when the audience first meets her, as an "internal" character. "She keeps to herself," she claims. "She keeps everyone at arm's length."

The catalyst for her passage toward freedom is fellow captive Caesar, played by British actor Aaron Pierre. "Caesar to me is a young man who has a great understanding of self, and a great understanding of his own beliefs and what the world should be," Pierre states. "He's definitely somebody who really takes in his surroundings and analyzes his environment. And I think he builds this encyclopedia of his experience of the world with every interaction and every movement he makes."

The story kicks it into high gear when the two characters seek salvation through the titular Underground Railroad, which in the show is an actual subterranean transport system created to assist runaways.

Mbedu and Pierre connected over Instagram before shooting began for what would become a long production.

"It's like we had known each other for the longest of times," confesses Mbedu, "but I think it's because we connected and understood what it meant to be in this project together telling these types of stories."

Adds Pierre, "What was really beautiful about our working relationship is that we completely trusted one another… We needed that [trust] because of the content we were dealing with and how much we were giving [of ourselves] when we were doing this project."

When discussing Cora's perilous decision to flee a life of chattel slavery, Mbedu puts its bluntly. "Thinking about freedom was actually thinking about committing suicide. It felt like a death sentence, because running away and being caught would mean you being killed," she declares. "When she finally steps out of the plantation and she's seeing the world, everything she's experiencing, she's experiencing for the very first time, which is why everything feels so much bigger than what it is, so much freer."

Playing Cora left a lasting impression on Mbedu, allowing her to reconcile her own past and achieve a certain catharsis. "Through this character, I have found healing I didn't know I was in need of," she reveals. "There are a lot of dark moments for her, but she brought about a difference within me. It wasn't just about empathizing with her — she touched parts of me that I didn't recognize needed to be touched and comforted."

While Caesar's path to freedom is cut tragically short, Pierre relished depicting his harrowing journey. "One thought I had throughout the process, which I continued to have, is that the Black diaspora has experienced devastating hardships and yet continues to overcome and rise and flourish. And to me, this story gives a powerful insight into the magnitude of that strength."

The Underground Railroad is now streaming on Amazon Prime Video.

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