Tarantino is at the top of his form with ‘Once Upon a Time . . . in Hollywood’

Brad Pitt and Leonardo DiCaprio in “Once Upon a Time . . . in Hollywood.”Andrew Cooper

We walk on thin ice, always. Beneath the ice is everything we ignore in order to get through the day: death, decay, despair, disease. Chaos, in other words — the infinitude of random things that can reach out and take us at any second. The car we didn’t see. The killer we don’t know.

The ice is made up of society and culture, patterns and art, rules of behavior and conventions of storytelling. And movies, of course. They all allow us to believe that order exists and that it can protect us. It can’t, but not many of us want to live without the illusion.

“Once Upon a Time . . . in Hollywood” is very much about these things, all while being a Quentin Tarantino film and one of his best. The director is among our most devoted, if prankish, priests at the altar of cinema, and he understands that the movies are essential to making sense of an insensible world. He knows they’re crafted, crowd-sourced dreams of hope, of things working out instead of falling apart. And he pits the illusion of storytelling against the chaos of history until one of them has to cry uncle, and maybe not the one you think.

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The movie unfolds in the film industry of 1969, as the studio era is dying and the blockbuster years have yet to begin. The central figures are Rick Dalton (Leonardo DiCaprio), a movie star who has seen better days and is reduced to villainous guest shots on TV shows like “Lancer” and “The FBI” and Cliff Booth (Brad Pitt), Rick’s longtime stuntman, gofer, therapist, and friend. Both once thought they knew how the town worked, and both are being left behind by a rapidly changing industry and culture. Cliff is dealing with it OK, Rick rather less so.

The byplay between DiCaprio and Pitt is delicious and finely drawn — you’d better believe Tarantino knows he’s dealing with two of our last old-school movie stars and sneakiest actors. Rick is a pampered diva with a stammer and a drinking habit, but when he turns on the charm for the camera, he’s still bulletproof. Cliff is cooler and supremely capable; he has a tragedy in his past — or is it a crime? — that keeps other people at a distance, and that’s how he likes it.

Leonardo DiCaprio plays a movie star who has seen better days.Andrew Cooper

Tarantino gets the rhythms of late ’60s Hollywood exactly right, as well as the colors, sounds, fashions, slang, pop hits, and long-forgotten advertising jingles. If you’re the appropriate age, “Once Upon a Time . . . in Hollywood” will be a 2½-hour Proustian madeleine of entertainment culture, the kind of thing that puts you into a blissful nostalgia coma. Or maybe not: Cliff lives up in the Hollywood Hills, on Cielo Drive, and his new neighbors are the film director Roman Polanski (Rafal Zawierucha) and his actress wife, Sharon Tate (Margot Robbie). Somewhere out in the dark, the Manson family is gathering. Evil is on the wind, but no one seems to notice.

“Once Upon a Time . . . in Hollywood” follows Rick and Cliff around town, together and separately, as they knock their heads against a business that no longer wants them. We get glimpses of shyster agents (Al Pacino) holding up the bar at Musso and Frank’s, TV cowboys (Timothy Olyphant), Steve McQueen (Damien Lewis), and an eerily self-possessed child actor (Julia Butters, a real find) who comforts Rick when the mask slips and he briefly comes unglued. Tarantino regular Kurt Russell has a dandy flashback as a gruff TV stunt director overseeing a roster of journeymen character actors much like his own dad, Bing Russell, who appeared in hundreds of cop shows and westerns back in the day. And a scene between the unflappable Cliff and a pompous young Bruce Lee (Mike Moh) on the set of “The Green Hornet” TV show is a ripely entertaining diversion.

Margot Robbie in “Once Upon a Time . . . in Hollywood.”Andrew Cooper

But Tarantino also follows Robbie’s Sharon Tate on a parallel track, as the starlet makes her rounds of a city that is at last her oyster. She ducks into a Westwood movie theater showing the Dean Martin spy spoof “The Wrecking Crew,” where she watches herself up on the screen with a wondrous disbelief. She’s famous now, and untouchable. Robbie has little dialogue yet she’s very touching; as you watch Sharon, you know she’s the story’s sacrificial lamb. At one point the soundtrack fills with the sounds of the Rolling Stones singing “Baby, baby, baby, you’re out of time,” and the sentiments roll out from Tate to Rick, Cliff, and an entire century of make-believe poised to come shuddering to a halt.

For all the fond evocation of time and place, kitsch and culture, this is a movie about dread — about the demons in the hills sharpening their knives. A marvelous, taut centerpiece scene has Cliff giving a lift to a flirtatious Mansonite (a live-wire Margaret Qualley) back to Spahn’s Movie Ranch, the decrepit western film set now overrun by Charlie’s girls. There are small, sharp turns by Lena Dunham, Bruce Dern, and a dead-eyed Dakota Fanning as Squeaky Fromme, but Manson himself (Damon Herriman) is nowhere to be seen in this sequence. It doesn’t matter; he’s everywhere.

“Once Upon a Time . . . in Hollywood” is explicitly about the stories that a massive 20th-century entertainment machine created in order to give us decades of happy endings. It’s about the anxiety and paranoia that existed behind the screen as a matter of daily business. And it’s about how all those happy endings and all that illusion still couldn’t keep chaos from erupting. The way Tarantino sees it, the Manson murders were the inflection point that finally punctured Hollywood’s dream of invincibility — that changed how movies told stories and how they dealt with violence. Why hold back on blood and horror when the real world can’t?

Al Pacino in “Once Upon a Time . . . in Hollywood.”Andrew Cooper

The final act of the movie is its most problematic, even as many will find it viscerally powerful. Manson family members Tex (Austin Butler), Katie (Madisen Beaty), and Sadie (a fearsome Mikey Madison, of TV’s “Better Things”) move up the dark of Cielo Drive with carnage in their eyes, at which point events begin to diverge from the record. I can say no more other than to note that the brutality that ensues verges on the gleeful, glib, and cartoonish, in ways that may be intended and ways that may not, and that the memory of the dead feels vaguely sold out for an evening’s catharsis.

And yet “Once Upon a Time . . . in Hollywood” is still a fairy tale (as those ellipsis points in its title imply), and the movie recovers its balance with a tremendously graceful final scene and farewell image that stands as Tarantino’s vision of an alternate history, one that runs right up to today. In this film’s Rabelaisian push-pull between reality and movies, chaos and make-believe, the darkness beneath the ice and the illusions we concoct in order to stand atop it, he comes down firmly in favor of the second half of the equation. And, honestly, who’s going to blame him?

★ ★ ★ ★

ONCE UPON A TIME . . . IN HOLLYWOOD

Written and directed by Quentin Tarantino. Starring Leonardo DiCaprio, Brad Pitt, Margot Robbie. At Boston theaters, Coolidge Corner, Somerville, suburbs. 165 minutes. R (language throughout, some strong graphic violence, drug use, and sexual references).