2014, PG-13, 128 min.

It’s been 50 years since Martin Luther King Jr. led some 8,000 people on a march from Selma to Montgomery, Ala. At the end of the march, the culmination of a three-month campaign of protests for equal voting rights for African-Americans in the South, King stood on the steps of the state capitol and delivered his famous “How Long, Not Long” speech. In it, he says, “Yet, Selma … became a shining moment in the conscience of man. If the worst in American life lurked in its dark street, the best of American instincts arose passionately from across the nation to overcome it.” In “Selma,” director Ava DuVernay chronicles those three months in 1965, and the interplay of light and dark and tragedies and triumphs, that characterized them. Not quite a historical drama and not quite a biopic, “Selma” is something of a mosaic, assembling the bits and pieces and people and places together into a cohesive picture. It’s a stunning, powerful, complex film, a movie unafraid to look for shades of gray in subjects that are so often reduced to one-note types.

“Selma” is satisfying in part because DuVernay and screenwriter Paul Webb avoid a lot of the usual traps found in historical dramas. The film opens with three short scenes: one of Martin Luther King, Jr. (David Oyelowo) and his wife, Coretta (Carmen Ejogo), together in Oslo, Norway, before he receives the Nobel Peace Prize; a scene of Annie Lee Cooper (Oprah Winfrey) at the Selma courthouse as she attempts to register to vote, only to be denied; and another showing the 1963 bombing of a black church in Birmingham that killed four young girls. From the start, DuVernay makes it clear that “Selma” is not a King biopic, nor is it a chronicle of the civil rights movement as a whole. Though King is the film’s protagonist, his work is the result of a collaborative effort, built on the sacrifices of those who came before him, and though Selma was a watershed moment, it was part of a larger struggle.

Oyelowo’s King is confident, yes, but just as crippled with doubt and uncertainty.

Though “Selma” works well as a narrative, its strengths lie in its individual scenes. Oyelowo anchors most of them — his portrayal of King is rich and nuanced. It would be easy to lionize King, to cast him as supremely confident and infallible, but Oyelowo and DuVernay opt for a fuller portrait. Oyelowo’s King is confident, yes, but just as crippled with doubt and uncertainty. When Corretta visits King in Selma’s jail to tell him she met with Malcolm X, we see a flash of jealousy and pettiness from King. A later scene, perhaps one of the best in the film, finds Coretta confronting her husband about his infidelity. She asks if he only loves her, and DuVernay lingers on Oyelowo as he pauses for what seems like an eternity before replying.

What’s best about Oyelowo’s performance is that he doesn’t go for imitation. He gets the broad strokes of King’s mannerisms and speech down and uses sheer charisma and talent to fill in the rest. DuVernay was unable to secure the rights to use King’s speeches in the film, and so she wrote the speeches featured in “Selma.” They’re not King’s words, but they’re so close that, when Oyelowo stands before a crowd or a congregation, you believe they’re from the man himself.

Other characters receive a similarly complex treatment (though it’s a shame that Ejogo doesn’t have more screentime as Coretta — her performance is fantastic). Tom Wilkinson perfectly captures Lyndon Johnson, a president caught between his desire to do what’s right and the realities of politics, and Stephan James is brilliant as John Lewis, a student organizer who comes into his own as a leader during the Selma marches. Wendell Pierce, Andre Holland, Omar J. Dorsey, Ruben Santiago-Hudson, and Colman Domingo are all great as King’s Southern Christian Leadership Conference allies — a scene in which they debate the root causes of voter suppression (the poll tax, literacy tests, voter sponsorship, etc.) is both incisive and great fun to watch.

DuVernay treats her characters with respect, but not undue reverence.

It’s in these moments that “Selma” is not so much King’s story as it is an ensemble film, one that concerns regular people, not important historical figures. When King and the SCLC members arrive in Selma, they sit down for an impromptu meal and some gentle ribbing. King smokes and scratches out speeches in a notebook; he’s phenomenally media-savvy, yet denies there’s any calculation behind his plans in Selma. DuVernay treats her characters with respect, but not undue reverence.

This is DuVernay’s third feature film, and, as such, it’s rough around the edges. Some scenes don’t quite work, and a framing device that uses FBI surveillance tapes to connect sequences often feels clumsy. But “Selma” succeeds despite those minor flaws. DuVernay has directed a number of documentaries, and at times, “Selma” has that feel. The “Bloody Sunday” sequence, in which protestors march across Selma’s Edmund Pettus Bridge and are met by a gang of state troopers and posse members armed with nightsticks, tear gas, and whips, is both brutal and breathtaking. It’s an unsparing scene in a film that never shies away from the consequences of racism and violence, and even if the rest of “Selma” paled in comparison (and it doesn’t), the sequence alone is enough to cement DuVernay’s place among this decade’s most promising directors.

But it’s important to remember that with “Selma,” DuVernay isn’t acting as a documentarian. Those seeking complete accuracy in “Selma” will have to look elsewhere, and that’s DuVernay’s point. Under the guise of heroes are regular women and men, and beneath the sweep of history and the drama of a great moral struggle are trying days and lonely nights when uncertainty and fear whisper from the shadows. History will fill in the details, but it is art, and films like “Selma,” that prompt us to shine a light on that darkness, and to do something about what we find.