Wunmi Mosaku still has an ugly scar from filming a pivotal scene in I Am Slave.

The 24-year-old Nigerian-born actress shows me her hand. A hook-shaped mark snakes along the fleshy edge of her palm.

“It's not very pretty but it's half of a heart so I'm going to get my husband, when I get married, to get a tattoo of [the other half] and we'll put it together,” she says with a laugh.

In the British drama, which is screening at the Toronto International Film Festival, Mosaku plays Malia, a young Sudanese woman who is kidnapped at the age of 12 and sold into slavery. On the first day of filming in Kenya (which doubled as Sudan), Mosaku did a scene where her character sees her father from a second-storey window.
“It was so emotional for me because my dad left when I was eight. It was like eight-year-old Wunmi and 12-year-old Malia all in the scene,” she says. “I see my dad for the first time and I'm running through the corridor and turn the corner. I turned the corner and I just went through a shop window.”

She was taken to the hospital for stitches. “I felt like it was my comeuppance for feeling on top of the world.”

This is her first starring role onscreen.

“I walked onto the set and I thought, 'This is the best day of my life.' And then you remember that it's someone's life. You think, 'I'm benefiting from someone's misery and torture.' ”

I Am Slave is based on the real-life experiences of Mende Nazer, who was abducted and forced to work in a London home. Directed by Gabriel Range (Death of a President), the film was shot in 29 days in Kenya and in a London home, close to where Nazer was kept. It ends with a sobering figure: An estimated 5,000 people work as trafficked slaves in the United Kingdom.

Mosaku is amicable and chatty, much unlike her character Malia who has little dialogue. “I was always looking at people straight in their eyes and Gabriel would say, 'You're a slave. You've not done that since the day you were bought.' It was hard to get my head into that mentality.”

• I Am Slave screens Sunday, Sept. 19 at 12:15 p.m., at Varsity 8.