In the relatively short amount of time between seasons one and two, Underground went from being a visceral exploration of one of the darkest chapters in American history to a show with a shocking degree of contemporary relevance. The small matter of the 2016 presidential election and its outcome revealed just how much the United States is still struggling to deal with the lasting social and legal effects of slavery.

"I think that there is definitely a DNA in America that seems to be coming back consistently," Underworld co-creator Misha Green says.

"That idea that when there's progress, there are people who want the old way to come back with a vengeance. And I think why it was important for us to make this show and tell this story is to show that there are ways to fight back.

"We were shocked last season by how many connections were easily made. When we really started diving into the research and the history, we would be like, 'this seems just like what's going on right now with minimum wage, doesn't it?'"

Set in the pre-Civil War "Antebellum" era in the mid-19th century, Underground takes its title from the Underground Railroad, a network of safe houses and shelters that helped ferry fugitive slaves from the Southern states to the free North.

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Season one detailed the daring and bloody escape of a group of slaves from a Southern plantation, lead by the plucky and resourceful Rosalee (Jurnee Smollet-Bell) and the broody, hulking Noah (Aldis Hodge).

Although Rosalee is now in the free North, most of her fellow escapers weren't as lucky, and she was forced to leave her mother and brother behind. When we rejoin her at the beginning of season two, she's teamed up with Harriet Tubman, an iconic real-life figure in the history of the Underground Railroad played by Aisha Hands.

"I've been on the road with Harriet Tubman, learning the ropes," Smollet-Bell explains.

"She's teaching me how this complex network works and my plan is to go back and get my family, go back the 600 miles. In season one we were running away from the danger, in season two, we're running towards it."

The Rosalee of season two is somewhat more of a badass than when she was first introduced.

Still shot from Underground. Photo / Steve Dietl
Still shot from Underground. Photo / Steve Dietl

"Now she's wearing pants and she's got a gun strapped to her leg," says Smollet-Bell.

"Rosalee definitely has evolved from a citizen into a soldier. When we met her in the first episode of season one, she was in the house. Now she's right in the middle of it and it's about really how much is she gonna stick her neck out."

It's not just her family that Rosalee is going to stick her neck out for - she's also committed to rescuing her beloved Noah, who is currently imprisoned.

"When she got to the North, she and Noah realised that freedom ain't so free, and we lost everyone. We made it, but they didn't. And I can't live with that sort of burden. And so all that's going through my head is there would be no other option for me than to try to rescue Noah and try to get my family back."

Smollet-Bell agrees that the show's subject matter has an increased relevance in the current political climate.

"I think you'll see a lot of people inspired to rise up, because, unfortunately, we have people who want to bring us back to a nation that we have grown out of. They want to bring us back to a different time where injustice and hate was normal. And I hope our nation is inspired to not allow that to happen and to not allow them to take our country back to the old days.

"We've grown so much. We've got so much work to do, we've got so far to go, but we need to keep moving forward."

Despite the recent rise in the number of acclaimed mainstream movies and television shows that are willing to address difficult subject matter, Green says getting Underground made was an uphill battle the whole way.

"People were very concerned with this being a 'slavery' show," says the former comic-book writer. "And we've always said, 'It's not about the occupation, it's about the revolution.' We make up these dystopian societies, like The Hunger Games, where everybody's fighting against the capital.

"You can look back into our history and this was happening for real, real people were doing it, and for me that just makes it more exciting. This is real, this is not made-up. And we can look at it and understand how to move forward by going back and looking at it. So for me it was always a thriller."

• Season two of Undergound premieres on Lightbox tomorrow. Season one is currently available to stream.