There’s a moment in “Judy,” about the late Hollywood queen Judy Garland, where you’re watching a thriller.

In a force-of-nature performance, University of Texas alumna Renée Zellweger plays the entertainer toward the end of her life, transforming into a bundle of pick-up sticks arranged precariously inside a sheath of mod fabric. And in the moment about which I’m talking, Garland is inebriated and barely standing. She’s just been pushed onto the stage for the opening night of a last-chance gig in London. She starts singing “By Myself.”

As the music builds, so does her hesitant voice, inching up to that gale-force (sorry) wind that you'd expect. All the while, she tremors and twitches, and her voice hits like a pick-axe, sending shards of flint into the air. Zellweger makes her eyes wider and wider as the seconds pass, even under blinding lights, like Judy can’t believe that she’s actually singing the song. It’s transfixing. She can’t possibly stick the landing, can she?

She does. She kills. And when it’s done, she folds over herself under a coil of cigarette smoke, like a car that just barely made it to a desert highway gas station before the radiator overheated.

That song might be the most stressful and most satisfying thing you see on-screen this year. And Zellweger’s Judy Garland is certainly one of the best performances you’ll see.

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“Judy,” directed by Rupert Goold and based on the stage play "End of the Rainbow," tells the story of Garland on the way down. It’s 1969, and the superstar is trying desperately to hold things together for her young kids, including Lorna Luft (Bella Ramsey, aka Lady Mormont from “Game of Thrones").

There’s no holding anything together at this point, though. Garland is boozing hard and addicted to the upper and downer pills foisted on her as a child actor. She’s functionally homeless, at one point making a star appearance at a swinging late-night party thrown by starlet daughter Liza Minnelli (Gemma-Leah Devereux, doing it right) just because she has nowhere else to go. People say Judy’s unreliable and uninsurable, and those are the people who like her. The tragedies of her life have finally shaken hands and decided to bear down their hardest on a woman who only ever wanted to use the talents that God gave her. “Ambitions gave me the most terrible headache,” she says wryly.

So, without work in America and trying to make enough money to keep custody of her kids, Judy sets off toward the only booking she can get: a five-week run at a London nightclub, seemingly doomed to fail.

“Doomed” is the million-dollar word for a flick like “Judy,” where you know what’s going to happen before you sit in the theater. (Garland died in 1969 from an overdose.) That’s why it’s impossible to oversell the work Zellweger does. This is not a perfect movie, but any shortcomings you could pluck out seem so trivial when you consider the size and the decency in her performance. Judy, at this point in her history, is not someone with whom you’d like to spend too much time. She’s destructive, she’s defeatist, she’s needy. She’s infuriated when a hotel clerk kindly informs her she’s out of money. She refuses to rehearse with her bandleader (Royce Pierreson) out of barely masked fear.

But the movie sticks a finger in your face: How dare you think you’re better than her? In Zellweger’s hands, Judy is also genuinely warm. She loves her children and thinks of them first, even when she’s white-knuckling it herself. She has a battle-worn wit and is a hoot at parties. When Judy’s on stage (on a good day, at least), Zellweger plays her with a full-body gulp, sucking up as much of the energy she gets from performing as she can. It could always be the last time. She walks through the film like a woman on her way to the end of the plank. She knows how all this ends, deep down, even if no one else says it out loud.

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Goold also executes some tricky calculus when it comes to the star’s relationship with her gay fanbase. To a certain generation of gay men, Garland and her movies were lifelines, lighthouses when their existence was pathologized and criminalized. “Judy” could have just winked at this relationship, but instead devotes an extended scene to the singer’s stage-door encounter with a pair of gay fans, which turns into a surreal, tender night. It’s knowing and never maudlin.

The movie also weaves into the plot a series of flashbacks to Judy’s days as a teen star at MGM. Darci Shaw plays the young Judy, a scared kid thrust into a hollow machine of diet pills, fake boyfriends and body shaming. The scenes fill in the necessary background of the star’s life, and the throughline is painfully clear from 1940s abuse to 1969 ruin. It’s hard to not feel like these moments are broccoli, though, when you have to take your eyes of Zellweger.

The whole cast orbits the singular main turn, but everyone gets a good bit or two in, including Finn Wittrock (who’s made a career of playing problematic hunks) as Judy’s last husband, Mickey Deans, and Jessie Buckley as her put-upon minder in London. None of them would get half as much mileage out of their characters if not for the stunning production and costume design. And of course, there's the faintest whiff of camp floating in and out of the picture, which is just how it should be.

The title says it all, though. This is Judy’s show, which means it’s Zellweger’s. There have been plenty of rise-and-fall star stories told throughout Hollywood history, but to me, the nearest viewing experience to “Judy” I can think of is Asif Kapadia’s 2015 documentary “Amy,” about soul singer Amy Winehouse. In that film, you see a woman of immense talent be taken advantage of at every turn by the very people who should have been looking out for her. So it is with “Judy” and its radical empathy for a woman trying her best, even when she's expected to perform small miracles with a microphone.