Author Yaa Gyasi is shown in this undated handout photo. THE CANADIAN PRESS/HO - Michael Lionstar

TORONTO - While touring a slave castle in her birthplace of Ghana, Yaa Gyasi gained fresh insight into a harrowing chapter of her homeland's history.

While visiting the Cape Coast Castle in 2009, she first learned that local women would be married off to British soldiers. Her tour guide then took her down to the dungeons where an alarming portrait formed in her mind.

"I was really just struck by the juxtaposition," said the soft-spoken California-based author during a recent visit to Toronto.

"The idea that there could be people walking around above free — Ghanaian people walking above free — and people down below who could be sent along the Middle Passage and didn't get a chance to know each other or face each other."

In her acclaimed debut novel "Homegoing" (Bond Street Books), Gyasi further crystallizes the contrast in a sweeping family tale spanning centuries and continents.

The story begins with tracing the divergent paths of half-sisters Effia and Esi, each unknown to the other, who are born in two different tribal villages in 18th-century Ghana.

As Effia lives a life of luxury married to an English colonist in the Cape Coast Castle, Esi's is one of sheer horror as she is imprisoned in a dank dungeon in sub-human conditions before being shipped to the U.S. to be sold into slavery.

The story continues to unfold through the eyes and stories of their descendents.

Gyasi said she originally wanted to write a more traditionally structured novel that takes place in the present. She then realized she was much more interested in seeing the themes of slavery, colonialism and institutionalized racism in America explored over a long period of time.

"I felt if I just had the beginning and the end and didn't include the middle then it would be easy for people to come away not feeling the accumulation of the weight of time on the characters who were living in the present," said Gyasi, who was raised in Huntsville, Ala., and turns 27 on June 29.

"Once I decided that, I realized I wanted a structure that let me stop in as many decades as possible."

Gyasi admitted there were moments she had to step back and take a break from researching and writing "Homegoing" as she plunged into dark, weighty subject matter. But she retained perspective by remembering the real lives impacted by such haunting life experiences.

"There were real people that had to live in that dungeon for three months at a time with no air and no light," she said.

"In a way, it felt like I had a responsibility to them to not look away and to not let other people off the hook so that they can't look away. Because if these people had to live it, then we kind of have a responsibility to them to remember it."

And despite the subject matter central to the story, "it's not all sad," she noted.

"There is a lot of joy in this book, I think. And even if not joy, then the kind of feeling of fullness that you get when you see a family member again that has been missing. I think that's one of the feelings I wanted to come across."

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News from © The Canadian Press, 2016