By Jeff Labrecque
Updated October 14, 2014 at 04:00 PM EDT
Focus Features

When The Theory of Everything debuted at the Toronto Film Festival, audiences couldn’t stop talking about Eddie Redmayne, who generated instant Oscar buzz for his portrayal of Stephen Hawking, the British cosmologist who’s spent most of his adult life in a wheelchair and speaking through a computer. The praise is well-deserved.

Hawking might be the story, but the film is based on the book of his first wife, Jane, played by Felicity Jones. They married in 1965, shortly after Hawking was diagnosed with autoimmune disease and doctors estimated he only had two years to live. With her unflagging devotion, Hawking went on to contribute some of the most important scientific ideas of the 20th century, and Jones had to portray Jane between the ages of 18 and 45.

There’s a risk that Jones’ nuanced portrayal will be overshadowed by Redmayne’s more-showy physical performance—just as Tom Cruise and Denzel Washington weren’t immediately rewarded for their exceptional work in Rain Main and Philadelphia, respectively. It would be insufficient to call Jones’ Jane the “good woman behind the great man,” because her story arc is just as compelling as Stephen’s—perhaps more so. “I know what you think, that I don’t look like a terribly strong person,” Jane says in the film. “But I love him, and he loves me. We’re going to fight this illness together.” Noble words—but mere words—it’s Jones’s powerful presence as a resilient woman that successfully captured something true, something real.

In a new behind-the-scenes trailer, director James Marsh and his two leading actors focus on the Hawkings’ extraordinary relationship, and Jones spoke to EW about her relationship with the real Jane Hawking.

EW: You did a lot of homework to play Jane. Am I correct in saying that Jane was the first role you’ve played where the real-life person was still alive and available for you to meet?

FELICITY JONES: It was really daunting because Jane is the first person I’ve played who’s a real person who’s alive and was going to actually see the film. That really raises the stakes, because you want to do them justice—and especially someone like her, who I was just so in awe of.

Stephen Hawking is a global celebrity and Eddie’s performance has attracted much of the publicity. But the film is very much Jane’s story. Did you start your research with her book?

Yeah, it was a full-frontal attack, really, on every level. The book was part of my research. Then, after reading that, I went to meet her—which was an extraordinary thing. You don’t want to do an impersonation, but you want to inhabit their soul in some way. So it was about trying to capture all those elements of Jane. It started with her voice actually. Jane has a very particular way of speaking—a quite high-pitched, careful, academic voice—that I thought, if I can get that, then I can get her. So I worked with a dialect coach and recorded her voice and would find bits and interviews where she’s speaking, and I’d watch her over and over again to try and get it.

What was your meeting with her like?

I remember I went around to her house and she very kindly cooked me dinner, with her husband Jonathan. We sat and talked for a long time about Stephen, about their relationship. She showed me these old slides of when they first met, so I felt like I was getting this real invite into her life.

You mentioned her voice, but was there other things that you picked up in meeting her that you simply couldn’t have learned from just reading her book?

Well, she’s someone who’s very decisive. She’s someone who I realized doesn’t take no for an answer. She’s got an incredible core strength to her, and that was important. She actually has an interesting philosophy, where she believes in making a commitment to something. And if you make that commitment, then you stick to it. And that helped me understand her bold decision in taking on the illness—because Stephen and her hadn’t been dating for that long [when they married]. She loved this man very much, but also at the same time, I think she felt a strong sense of duty as well.

When you met her, did it feel as if she was sizing you up as well?

Absolutely. Definitely. It was two-way relationship. And actually, after we’d had dinner and spent time talking, when I left, she very sweetly said, “I completely trust you,” which was a special thing of her to say.

Did she talk about the tone of the film and things that were important to her in terms of translating to the screen?

I feel like she trusted us‚ trusted James. But I think what was very important, both Stephen and her have a very, very dry sense of humor. They’re really sharp witted, and so, Eddie and I constantly would be looking for places to find humor and bring that to the screen. Because in a way, Stephen’s illness is the least interesting thing about him. He’s an incredible charismatic, charming, witty man, and it was always important to find the joy in the situation, which was true to how Jane and Stephen behaved throughout the relationship.

Had you worked with Eddie before?

We both worked for Michael Grandage at the Donmar Warehouse, and were both huge fans of each other for ages. I’d always wanted to work together, and I guess, was just waiting for the right project. We have very similar ways of working, we both like to prepare a lot, lots of discussion and collaboration. It felt like a very special film in that respect—James made us feel very included with everything. I came in and read with James and Eddie, and something just worked in that room. It felt very right. It felt like something special was happening.

Eddie did a lot of work to capture Stephen’s physical deterioration, but Jane’s changes are much more subtle. You’re the strong one, and you have to reflect what’s going in a very different way. How did you calibrate that, from start to finish.

Wow, that’s a big question. A huge amount of it is instinctive. It’s understanding what someone’s ideology is, and how that belief system effects her interaction with the world. Her religion was very important. I’m not religious myself, but I went to a local C of E church in London, to just try and absorb what that person’s impulses are, what is their headspace, what’s their frame of reference. At the same time with Jane, I was trying to show how she shifts and changes over many years. And actually, I found her much more fun to play when she’s older because she gets a lot more strict. She doesn’t pussyfoot around people. She’s very direct, in a way, that’s very different from when she’s young and quite shy and earnest and careful.

Eddie’s biggest challenges in playing Stephen were mostly physical, but what was the hardest thing about playing Jane?

All the time, I just wanted to get Jane’s voice through. You know, sometimes playing the person in the background, it’s not the most glamorous role. I felt very strongly that she was an extraordinary woman who had a practical side to her, an efficiency. You know, when doctors said that Stephen wasn’t going to live more than two years, she wouldn’t take no for an answer and had incredible tenacity. But then at the same time, she had huge reserves of love and kindness, and I just wanted to get all of that on the screen and that was always my priority.

Has Jane seen the film?

Yes, I spoke to her about a week or so ago, and she was very complimentary about it. She’s looking foreword to coming to the premiere, so I believe that’s the sign of approval.

The Theory of Everything opens in U.S. theaters on Nov. 7.