12 Years a Slave is agony in the fullest sense of the word. Chronicling the life of Solomon Northup, a free black man from New York kidnapped and sold into slavery in 1841, the film sees director Steve McQueen (Hunger; Shame) at the very zenith of his formidable artistic talent. It takes a horrific portrayal to capture a horrific institution. 12 Years is a mesmerizing, intoxicating tale of man’s capacity for both unspeakable cruelty and incalculable courage.

Solomon (Chiwetel Ejiofor) is first introduced as a prosperous and cultured family man. After temporarily traveling to perform with a pair of unscrupulous circus performers, one bad night of drinking is all it takes for him to wake up in chains. Initially, Solomon is defiant and indignant, as one might expect. “I don’t want to survive,” he says; “I want to live.” This attitude is quickly beaten out of him.

This, in fact, is the main reason why 12 Years a Slave is easily one of the most agonizing films of the year. McQueen has never been known to pull punches, and he certainly doesn’t here. The violence is swift, brutal, and often unexpected. There are several scenes so ghastly, so terrifying, that I trembled and flinched in ways I have never done before during a film. Yet, the pain one feels sitting in the audience is infinitesimal to the misery experienced by someone born and sold into slavery. This is the absolute worst aspect of the film’s on-screen cruelty: the entire time, one’s mind is racing with the words, “This once happened. People did this. People still do this.”

It is true that Solomon’s story is full of wickedly inhuman humans; as Paul Giamatti’s slave trader says, “My sentimentality extends the length of a coin.” Yet, this brutality also makes the flashes of courage all the more formidable and inspirational.

Lupita Nyong’o gives a breathtaking performance as Patsey, a slave encountered by Solomon once he is sold to the Epps plantation. Patsey is a raw personality within an equally raw film, and Nyong’o captures the character with a fullness and deftness that belies her relatively nascent career.

The other knockout performance comes from Ejiofor. He succeeds in imbuing the role of Solomon with gravitas and grace, but Ejiofor’s best moments are when the fragility of the character shines through. Solomon is neither hero nor saint, and Ejiofor’s portrayal is entirely human. The twin powerhouse performances of Ejiofor and Nyong’o are impactful even with an exceptionally talented supporting cast (including the always-on-form Michael Fassbender and Brad Pitt).

The smart screenplay by John Ridley is impressively nuanced, capturing much of the complex intersections of race, gender, and economic status that existed among slaves and slaveholders. Hans Zimmer’s score features deliciously dissonant percussive turmoil, in addition to the typical panoply of melancholic strings. These aspects, as well as the film’s impeccable pacing, editing, and cinematography, makes 12 Years one of the crown jewels at this year’s Toronto International Film Festival.

Here, Steve McQueen achieves one of the holy grails of cinema—12 Years a Slave holds up a mirror to the darkest forces of humanity, and forces us to look. I shed tears, not just for Solomon Northrup, but also for the countless souls who have suffered and continue to suffer under the barbarous practice of slavery. And judging by the chorus of sniffles rising from the audience, I wasn’t the only one.

12 Years a Slave received its world premiere at the 2013 Toronto International Film Festival, winning the People’s Choice Award. It is set to be released Oct. 18.