PBS’ new period drama Mercy Street, which launched behind the final season of Downton Abbey and already has been renewed for a second season, tells the story of two volunteer nurses working on opposite sides of the Civil War. “Part of the goal setting out was to tell a great American story that matched the quality and texture of other great PBS series,” co-creator/executive producer David Zabel said at Deadline’s Contenders panel, joined on the panel by co-stars Josh Radnor, Gary Cole and Shalita Grant.

As with WGN America’s Underground, the series was conceived with the desire to uncover real, untold stories from the Civil War era. “The real lynchpin (in the series) was the town of Alexandria, Virginia, which was a Northern-occupied Southern town,” Zabel explained. Within this “great melting pot” of a setting, Zabel could dig into drama affecting a wide array of characters across the Union-Confederate line.

Zabel noted the unconventional way that the series came together. “With PBS, (fellow co-creator) Lisa Wolfinger and I were able to develop the first six hours over four years, so it was a really nuanced, gradual process.” In casting the series, the creator said he was pleasantly surprised to find that there was a number of accomplished actors who responded strongly to the unusual, heavy material, which moderator Pete Hammond described as a mash-up of MASH and Gone With the Wind. “It was an unexpected, humbling experience because it wasn’t a splashy production, in the sense that it would be all over the press,” he said. “It was really about people falling for the material.”

What the actors responded to was the chance to explore the duality of a complicated cast of characters within a setting that is rarely depicted on screen. “I think in our compulsory education we’ve all had a Civil War course, but rarely do you go in depth with what that period was,” said Grant, who tapped into an experience studying slavery, the Civil War and Reconstruction at The Juilliard School to get into her character’s experiences.

Josh Radnor, best known for his portrayal of perpetual romantic Ted Mosby in How I Met Your Mother, appreciated that the show’s writing went deep into the grey areas of character, and of the Civil War in general. “I think a lot of TV writing is encouraged to go a little broad in terms of a defining characteristic—like, “this character likes shopping, and that’s what they are. It’s good to lean into contradictions.”

And, of course, for Radnor there was the opportunity to do something entirely different. “A morphine addicted surgeon in the Civil War was as far away from (How I Met Your Mother) as I could go, so I said, ‘Sign me up,’ Radnor said.