Some time after she agreed to play the legendary swimmer Diana Nyad, Annette Bening experienced what she calls a “come-to-Jesus moment.” To fully embody one of the most physically competitive athletes of her age would require a level of commitment that was just beginning to dawn on her. “My God. What am I going to do?” she remembers thinking. Bening hired a coach, the former Olympic swimmer Rada Owen, and began by talking through the basics—the unique strokes, the correct way to kick in the water. They went from there. All told, Bening trained intensively for about a year.

“We build these cages for ourselves in our brains about what we can and can’t do,” Bening says. “We get so used to that, that we sort of even forget that they’re there.”

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She’s talking about her character here, and the singular accomplishment of the 64-year-old woman who swam over 100 miles in one stretch, from Cuba to Florida, after years of unsuccessful attempts. But Bening, now 65, might as well be referring to herself here too. In the affecting biopic Nyad (hitting select theaters October 20 before Netflix starts streaming it on November 3), the Oscar nominee (American Beauty, The Kids Are All Right) delivers a powerhouse performance unlike any in her illustrious career. She dives into Nyad’s prickly personality and remarkable physicality with both the charisma of a movie star in her prime and the precision of a veteran craftsperson. “She wouldn’t take the role unless she was prepared to do the work,” says the film’s codirector, Elizabeth Chai Vasarhelyi. “That was daunting to her. She knew herself that she would have to learn to swim that way—and she wasn’t necessarily the best swimmer.”

Vasarhelyi helmed Nyad alongside her husband and creative partner, Jimmy Chin, in what marks their narrative directorial debut. Oscar winners for 2018’s Free Solo, the documentarians had been looking to try their hand at fiction filmmaking and were presented with a story rather neatly matching their established cinematic interests. “We love telling these stories where somebody’s pushing the edge of the human experience,” says Chin, a professional mountain athlete. “We hope when audiences leave the theater, they feel like they’ve gotten an expanded perspective of the human experience.” Vasarhelyi says that Nyad’s story “defies the frontiers of what you can imagine”—a solid one-line descriptor for this duo’s filmography as a whole.

Nyad has been a noted athlete since the 1970s, when her swims around Manhattan, New York, and in the Caribbean brought her national attention. At the age of 28, she attempted to swim from Havana to Key West, in the aftermath of the Kennedy-era travel restrictions being lifted, but, in part due to inclement weather, could not complete the task. She went on to write books and launch motivational speaking tours, but her athletic career faded as she got into her 30s and 40s. Then in 2010, at age 60, she firmly decided to finish what she’d started decades ago—and though she didn’t make it to Florida over several more attempts, eventually she did. “This film asks: What do we give ourselves permission to do in our lives?” Bening says. “Diana said, ‘I’m actually going to ignore all of these norms about what women in their 60s do.’”

Yet Nyad is no glossy tale of heroism and triumph. The film embraces its eponymous character’s complexity, presenting her as determined if abrasive, as caustic as she is relentless, and of a bracing intelligence matched only by her ego. That’s evident both in Julia Cox’s screenplay, adapted from Nyad’s 2015 memoir Find a Way, and Bening’s bold portrayal. And it comes alive through the beating heart of the film—the tricky, rich, hard-earned bond between Diana and her best friend and eventual coach, Bonnie Stoll.

In real life, Jodie Foster had known Nyad and Stoll casually for years. “Their quirky humor, familial banter, and all-around goodness just continually swept me off my feet,” the Oscar winner says. Their dynamic is why she wanted to make the movie and play Bonnie. In Nyad, the centering of two female characters of a certain age, both out lesbians, feels quietly radical. “Jodie brought her point of view as a queer woman in her 60s, and it was very helpful,” Vasarhelyi says. “It was always the intention to make a buddy movie. You can’t really separate Bonnie from Diana if you know them in real life.”

The film makes this case, as do Bening and Foster, whose chemistry is so irresistibly lived-in you’ll be stunned to learn it’s the first movie they’ve ever made together. “Annette is a scrappy San Diego girl, a no-frills team player who could probably whip up dinner for 20 off a campfire,” Foster says. “She’s effortlessly easy, loves big drooling dogs—me too—and doesn’t suffer any BS in the work department. I just loved her immediately.”

Vasarhelyi, Chin, and screenwriter Cox ran roundtable discussions with the two actors, digging deep into the project’s feminist themes. Then they rehearsed extensively, including for the movie’s logistically elaborate boat scenes, wherein Foster’s Bonnie and Rhys Ifans’s John Bartlett, the hired chief navigator, keep tabs on Diana as she swims for dozens of miles—and nears the razor’s edge of utter depletion. For the directors, blocking these sequences out with DP Claudio Miranda (Top Gun: Maverick) in very tight and specific spaces proved essential. For the actors, it’s where they could gear up for the arduous work.

“Annette faced all the hardest challenges. Swimming in the water for hours and hours, stomaching salt water, fluctuating body temperatures, wearing that weird silicone mask, long hours in every weather condition, day and night—and all of it in a bathing suit,” Foster says. “That’s my worst nightmare.” She remembers worrying about her costar from up above in the boat, as Bening just kept going in the Caribbean Sea off the windy coast of the Dominican Republic, where production took place. “I found myself bugging the ADs to get her out of the water for breaks. She just kept lifting her thumbs up saying she was fine. I was so worried her body would betray her iron mind, but it never happened,” Foster says. “That woman has the strongest will I’ve ever seen on a movie set.”

Bening first got into the massive tank built for the production before even being asked. On the eve of filming’s start, the crew prepared a simple safety test, with stunt doubles around to run the trial swims themselves. But Bening—literally and figuratively—dove right in. “I will never forget it,” says Vasarhelyi. “She got in the water and she took her first stroke and she swam across the tank—and everyone who witnessed that was like, Whoa.” Once filming started, Bening would swim for four, five hours a day, charting Nyad’s determination. “The physical performance that Annette was able to tap into for me was really incredible—of being able to decide, ‘This is what it’s going to look like 40 hours into a swim,’” Chin says. “We didn’t really coach that. I don’t know that you can!”

With standout supporting turns from both Ifans and Foster—she too got in great shape for Nyad, training on her own for about six months—it’s an impressive set of performances found by two first-time narrative directors. Chin says that their unique skills as documentarians could be applied to collaborating with actors. “Having worked with some of the top outdoor adventure athletes, skiers, snowboarders, surfers, climbers in the world, I’ve learned that it’s really about giving the talent faith to do what they do—creating the environment for them to be able to perform at their best,” he says. For a couple of actors at the top of their field, then, he and Vasarhelyi knew how to set the conditions.

Within the world of competitive open-water swimming, Nyad is a somewhat controversial figure. The veracity of her accomplishments has been questioned, since her claim of being the first person to swim from Cuba to Florida without any kind of enclosure has not been officially ratified. A few dozen people witnessed her swim, but the exact mechanics of how she pulled it off remain a point of contention. “As documentary filmmakers, the first thing we did was to look into some of these criticisms—and found that they weren’t valid,” says Chin. “Working in the realm that I work in, especially in climbing, there’s always the critics…and when you are at the forefront of your sport, you have a target on your back. Especially if you’re an outspoken athlete like Diana might be considered.”

The film, of course, goes to great lengths to paint Diana as a flawed figure of unimpeachable willpower. But she has a long history of not being believed. Nyad invests in her rise as a female athlete through that prism, giving weight to her allegation of being sexually assaulted as a child by her swim coach. Those memories are weaved into the present-day scenes of Diana chasing her miracle swim. “I’m just a little tired of the internet trying to tear down a woman who’s complicated and outspoken and owns who she is,” Vasarhelyi says. “We went to great lengths in the film to be able to live up to that. She is a complicated person who has a complicated life.” She says more broadly of their approach, “We don't say, ‘It’s based on a true story,’ we don't say, ‘It is a true story’—but it is a true story. It’s about this idea of truth.”

Nyad got involved in the film about her life early on, and assisted the filmmakers with those nitty-gritty details regarding long-distance swimming—how it feels, where your mind goes, why it so consumed her—but did not visit the set until the end of production, leaving them to make their own movie.

She did, however, spend a good amount of time with Bening, and left an impression on the actor. “We talked in a very deep way, in a very trusting way,” Bening says. “That meant a lot to me. I will always be grateful to her for that.” When Bening first encountered the swimmer’s story, she felt an instant connection: “Yes. Okay, I gotta do this. I gotta try to do this.”

The preparation and shoot was not easy. Bening’s nerves didn’t exactly abate. But in getting to know her subject, and in learning how to swim at such a high level, she came to understand the sport’s particular power. “I began to just completely fall in love with it because of how it affects your central nervous system and your brain—and that, for me, that’s why it gets addictive,” she says. “You reach a state where the mind stops chattering or criticizing or judging or planning. And suddenly everything quiets down.”

Foster observed this peace emerge within Bening, and could barely believe it. “Someday I’m going to teach her to complain,” she says. “I don’t know how she did it with all that swimming.” Bening offers a hint as she concludes: “I will definitely keep swimming. It keeps me calm.”

Interviews with Annette Bening and Jodie Foster were completed before the SAG-AFTRA strike began.

Nyad makes its international debut next month at the Toronto International Film Festival. Netflix will release the film in select theaters October 20 before streaming it beginning November 3. This feature is part of Awards Insider’s exclusive fall-festival coverage, featuring first looks and in-depth interviews with some of this coming season’s biggest contenders.