There’s a brief scene very early in Steve McQueen’s 12 Years a Slave, a wordless series of shots serving as a little prologue to the film and a flash-forward to a much later sequence. A black man eating his supper pauses as he fixes on the berries on his tin plate. He’s next seen in darkness, sharpening the end of a short stick and dipping it into the berry juice to write something before he stops and a look of great frustration and despair appears on his face.

The man is Solomon Northup (Chiwetel Ejiofor), an American citizen who was abducted and sold into slavery in 1841. The brief scene encapsulates his abysmally wretched experience in bondage for the 12 years of the title, which comes from Northup’s memoir, published in 1853. And that look on Ejiofor’s face is a dramatic precis of the actor’s magnificently evocative and engrossing performance. Without his brilliant work, McQueen’s movie couldn’t cohere dramatically as well as it does, or impart the humane feeling it sometimes achieves. As it is, 12 Years a Slave can sometimes seem redundantly violent or stuck on a bleak tangent. Ejiofor’s performance mitigates these moments and enlarges the picture’s emotions.

Following the outline of Northup’s published story, Solomon is introduced as a respected freeman in Saratoga, New York, a man who evidently makes a good enough living as a violinist to support a wife and two children in some comfort. He has apparently earned the friendly respect of the white townfolk. After seeing his family off on a trip whose purpose isn’t identified (McQueen and writer John Ridley are sometimes a little careless about details), Solomon accepts a handsome offer of employment in the District of Columbia from two strangers. He is drugged while dining with them in a Washington hotel, and awakes to find himself shackled in a cell, and then put on sale at a slave market. Purchased by a relatively benign Louisiana planter, William Ford (Benedict Cumberbatch), he becomes a sugar cane plantation field hand, as he strives to survive until some perhaps miraculous rescue.

But his intelligence and skills eventually leave him in a very dangerous conflict with a murderous, vindictive overseer (Paul Dano). To protect both Solomon and his own position with creditors, Ford sells him to Edwin Epps (Michael Fassbender), a reportedly hard man, who, it soon transpires, is an unbalanced and sadistic despot. Solomon’s efforts to survive become frighteningly more difficult in the face of Epp’s volatility and brutality. (It’s in this setting that those first images are repeated in a sequence that involves Solomon’s secret, dangerous literacy.)

12 Years a Slave is usually all too persuasive in its dramatization of incidents in Solomon’s long, vile ordeal. The antebellum recreations and dialogue regularly come off as authentic (although the racially integrated Washington hotel where Solomon dines with his two betrayers is an odd anomaly). But after the story leaves him at the unlikely mercy of Epps and his jealous, imperious, and eccentric wife (Sarah Paulson), the movie can seem repetitious. In some intervals it lacks real dramatic progress as Epps and Solomon are bound in their strange, violence-punctuated, master-slave relationship. The individual parts can be powerful but there’s a redundancy at times. There’s a semi-hermetic feel to some of this.

McQueen does catch some unusually striking and vivid visual compositions. Their beauty can be unsettling, even ominous when they appear between scenes of the slaves’ cruel burdens and the brutality that Epps and his ferocious wife can visit on them.

McQueen has elicited performances of a very high caliber. Besides Ejiofor, the standout performer is Lupita Nyong’o as Patsey, a slave woman Epps has a perverse yen for despite his wife’s incensed disapproval.

This film is going to be nobody’s idea of conventionally enjoyable entertainment, but it’s likely to long remain the definitive depiction of what historian C. Vann Woodward called America’s peculiar institution, and which remains its historical guilt

Watch the trailer for 12 Years a Slave