In the upcoming drama All I See Is You, Blake Lively plays a nearly blind woman whose sight is restored after an urgent, miraculous surgery. The character, Gina, then goes through a whirlwind of change, discovering new things about herself, her sexuality, and her marriage. It’s a fraught psychological affair, with Gina’s husband (played by Jason Clarke) slowly realizing that he misses the days when his wife was wholly dependent on him.

“It’s the performance that I’m most proud of,” Lively tells Vanity Fair.

Directed by Marc Forster, the film requires a lot of Lively, who appears in nearly every scene as her character transforms from a meek woman into a determined siren. Forster shapes the drama with experimental flair, featuring kaleidoscopic imagery and racy scenes that required Lively to appear partially nude on screen for the first time in her career.

That was so outside her wheelhouse that Lively almost never saw the script in the first place; her team assumed she would not be interested in a role that required nudity, and Forster was unwilling to remove it. “I thought well, he’s not unmoving. Let me read it and if it’s great, then I’ll [talk] him out of it.”

So Lively read the script, and instantly fell in love—nude scene and all. The way Forster had written it actually changed the way Lively viewed on-screen nudity: “I always find nudity distracting,” she says. “I’m very in love with my husband, but if there’s a pair of boobs out, I’m a human being! You’re like ‘boobs!’ It doesn’t mean I’m lusting for them, [but] when there’s naked boobies, you look at them.”

For character research, Lively consulted with blind friends and experimented with using blackout glasses. Throughout the film, the actress also has to wear a variety of contact lenses to show her character’s evolving states of visibility. In an act of true kismet, the on-set lens technician who worked with Lively had actually gone through something similar to her character’s experience, and was able to serve as an instant resource for the actress.

“I was really acting for her,” she says. “[I would ask] is this the accurate reaction? How do you feel? If I would make her laugh, or if I would make her cry . . . then I knew I was doing my job.”

The film took place and was actually shot in Thailand last year. Lively leapt right into the job just four months after giving birth to her second daughter, working grueling 19-hour work days. “I don’t remember a moment that we weren’t filming,” she says. “It was the most intense film I’d ever been on.”

When asked how one manages to keep up regular 19-hour work days, Lively laughs: “You just stop sleeping at night.”

All I See Is You hits theaters on October 27. Check out an exclusive poster for the film below.