Chiwetel Ejiofor, left, plays a free black man who winds up as the property of a slave owner played by Michael Fassbender. Chiwetel Ejiofor, left, plays a free black man who winds up as the property of a slave owner played by Michael Fassbender.

It’s one scene in “12 Years a Slave” that will win Chiwetel Ejiofor the best actor Oscar. Oh, the rest of his performance as Solomon Northup — a real-life, free-born black man who’s tricked, sold into slavery and sent to Louisiana — is enough to warrant the trophy, but that one scene locks it down.

Years into Northup’s captivity, much of it spent on the plantation of Edwin Epps (Michael Fassbender), Northup attends the funeral of another slave. As a spiritual repeats and repeats, director Steve McQueen leaves the camera on Ejiofor’s face for minutes, and the audience watches as Northup slowly breaks down.

“I was always aware there were these moments of chance, and that was one of them,” Ejiofor says of the unscripted images. “It came out of nothing. But I supposed the thinking behind it was, in the moment of burying the slave, I think that Solomon realizes that, for all his hopes and dreams and his attempts to achieve freedom, he may end up like this guy. And the other slaves might be burying him.”

Solomon has no shot at freedom. No one believes that he was born free and comes from New York. Even though he’s literate, he can’t write a letter — he’s forbidden to have paper or any writing utensil. Escape is essentially impossible. As Solomon comes to realize this, the stakes change for him.

“I always saw the story of Solomon believing he was in a battle for his freedom but realizing that he was in a battle for his mind,” says Ejiofor of “Children of Men.” “That’s a different kind of survival instinct. There’s a part of him that’s trying to give up on the dreams of getting back, but still finding a way to survive.”

Epps, Solomon’s owner, is renowned for his cruelty, and life on his plantation is consumed by the monotonous boredom of picking cotton. (“With cutting timber and sugar cane, there’s a physicality of letting something out,” Ejiofor says. “Aggression, frustration — there’s something to counteract that. But when you’re picking cotton in 108 degrees, there’s no sense of that.”) The monotony is interrupted only by sudden bursts of horrific violence and, among the slaves, moments of genuine connection.

“This story is about human beings,” the 36-year-old actor says. “As much as they can do these horrific things, there is always this hope, a yearning, a love. The camaraderie of the slaves themselves — they attempt to give each other kindness.

“There is so much that worries us about our inhumanity to each other,” he continues. “The fact that we have this humanity as well — Solomon is someone who holds that with him.”