“BlackKklansman” is the funniest Spike Lee movie in decades, a film of such wit, tension, passion and relevance that it is his most important work since “Malcolm X.”

This mostly-true story of a grim but ironic undercover sting of the Ku Klux Klan allows a filmmaker infamous for getting in his own way, condemned to low budget filmed stage shows, documentaries and movies-nobody-saw, to return to relevance with a thriller that’s epic in scope and satirical in its bite.

All it took was hot producer Jordan Peele (“Get Out”) and three extra screenwriters to get it made and rein in just enough of Lee’s excesses to get him back to making the sorts of movies he used to toss off with ease.

Ron Stallworth, subtly-played by John David Washington of TV’s “Ballers (and a tween extra in “Malcolm X”) was a straight arrow son of a career military man who became “the Jackie Robinson” of the Colorado Springs Police Department in the 1970s.

He endured the racism of his own department, first in the records room where the rookie was repeatedly asked for files on this or that “toad.” Colorado racist cops had given up the N-word for the T-word. Progress.

But a smart guy like Ron, with his Natural hair style and the ability to switch from his usual “King’s English” to “jive,” figures undercover work is where it’s at. And after much grousing from the more racist colleagues, and his prickly chief (Robert John Burke), he gets his chance. He wears a wire into ex-Black Panther Stokely Carmichael’s speech, invited to address the black community by the local college’s student union.

Stallworth was to spy on this “radical” who was “stirring things up.” The police were looking for an excuse to arrest the FBI target then going by a newly-taken African name, Kwame Ture. No dice there, the rhetoric wasn’t that incendiary, Stallworth insists.

But he passes muster with the undercover guys (Adam Driver, Steve Buscemi’s brother Michael Buscemi). And he does meet a “fine as red wine” sister, Patrice (Laura Harrier), whom he has to lie to even as he resists her crowd’s insistence on calling police “pigs.”

They have their reasons.

But it’s a glance at a brazenly-placed newspaper recruiting ad for the KKK that piques Ron’s interest and gets him on the phone. His “King’s English” convinces the voice on the other end of the line of his “white” legitimacy, his instincts tell him that these creeps are thinking big — and violent. All he’s got to do is convince his boss (Ken Garito), the chief and the rest of the “intelligence” squad to go along with it, and get a white cop to play the role he’s creating on the phone and infiltrate the KKK.

The skeptical, jaded Flip (Driver) reluctantly agrees.

“I’ve always wanted to be black.”

Lee, working from the real Ron Stallworth’s memoir, takes us into a world of virulent racists, paranoid gun nuts and delusional cranks, “The Invisible Empire,” whose members lay low, refer to the KKK as “The Organization,” The Cause.”

And they are planning “a big year,” something bigger than mountaintop cross burnings — “The highest hills get the most eyes.”

Ron, in the person of Flip, goes to redneck bar gatherings and backwoods shooting parties where the boys trot out their named firearms (“I call this one ‘Jew Killer'”) to riddle African American-shaped targets.

He faces the furious, ignorant suspicion of Felix, played in a fine, foaming-at-the-mouth fury by Finnish actor Jasper Pääkkönen.

And he debates Ron on the importance of what they’re doing.

“For you, this is a crusade. For me, it’s a job.”

Lee balances Ron’s work debates with his guarded arguments with the “Revolution is Now” Patrice. His patriotism has him ironically believing “America would never elect somebody like David Duke president of the United States.” He tests his own idealism with her, his belief  you can effect change “from the inside.”

Patrice, rousted and abused by the most racist local cops on the night of the Carmichael/Ture speech, doesn’t buy it. With her voluminous Afro and high profile in the community, she’s almost certainly on the KKK radar as well.

Lee steadily ratchets up the tension even as he’s never far removed from finding these dangerous men funny. Casting Topher Grace as the young Louisiana racist KKK Imperial Wizard Duke sets the tone, and works wonderfully. Black Ron has to call National KKK headquarters to see about his membership card, and shockingly, the Big D is who answers the phone and expedites the card.

“God Bless White America!”

The local group’s collection of secretive sympathizers in government and literal mouth-breathers warns White Ron that “a war’s coming.” Will Black Ron and White Ron be able to stop it?

Lee finds places to squeeze in his trademarks — his rolling reverse zoom, pointed political criticism and “Uplift the Race” sermons and lectures. They fit here. Alec Baldwin plays a man rehearsing a KKK film lecture in the movie’s heavy-handed and somewhat ill-fitting (but biting) opening scene. Lee gives actor Corey Hawkins, as Carmichael/Ture, minutes of mesmerizing screen time for his speech.

Ture’s speech doesn’t so much “turn” Ron as lay the out the distances between the races, and ways that gap has and hasn’t closed in 45 years. Harry Belafonte has a moving cameo, telling the story of a long-ago lynching his character witnessed to a rapt Black Student Union audience.

And Lee finishes with a flourish, hammering home the connections between the KKK then and now, racist leadership then and at the very highest levels now.

Those of us who have followed Lee’s work over the years embrace his strengths and his flaws. He shot “BlackKklansman” in a grainy, lurid blacksploitation style (period appropriate tunes) and texture and wonderfully balances the mockery of the racists with the grim realities of the true story.

But Spike never learned to drop the mike, leave the audience craving more. As with “Malcolm” and most of his signature films, he cannot bear to exit the stage, running “BlackKklansman” past its climax, sermonizing until the credits stop him.

At least he’s outgrown the tendency to have an actor turn to the camera and shout “WAKE UP!” at the faithful.

With “BlackKklansman,” the great touches overcome his two Achilles Heels. Let’s hope this reconnects the filmmaker with the wider big screen audience, because talent this mercurial has been a terrible thing to waste.

MPAA Rating: R, violence, profanity, racism

Cast: John David Washington,  Adam Driver, Laura Harrier, Topher Grace, Jasper Pääkönen, Alec Baldwin

Credits:Directed by Spike Lee, script by Charlie Wachtel, David Rabinowitz, David Wilmott, and Spike Lee, based on the memoir by Ron Stallworth. A Focus release.

Running time: 2: