Every awards season has one: that underdog movie that ends up battling with the studio heavyweights for Oscars glory - a Little Miss Sunshine, a Beasts of the Southern Wild or even a Boyhood. This year that mantle has been inherited by Room, Irish director Lenny Abrahamson's take on Emma Donoghue's beloved Booker-nominated 2010 novel about a young kidnap victim and her five-year-old son, fathered by their captor.
Already the film won the People's Choice Award when it played at the Toronto International Film Festival back in September - and it's now a strong contender for a Best Picture nod at the Oscars (six of the past seven Toronto audience winners have been nominated). It received Golden Globes nominations in Best Picture (Drama) and Best Screenplay and its star Brie Larson scooped the Best Actress award this week to add to the feeling that Room is this year's Goliath-slayer.
Larson, a 26-year-old Sacramento native, broke out two years ago as a young counsellor in Short Term 12. It's already been a killer 12 months for her, with roles in The Gambler, alongside Mark Wahlberg, and hit comedy Trainwreck, playing Amy Schumer's strait-laced sister. But Room's Ma is a rip-up-the-rule-book role, "the kind of performance that can elevate a career to a new plane", as Vanity Fair termed it.
"She blew me away," says Abrahamson. "She has this naturalistic quality on screen. She disappears into the character. She's luminous and holds the screen, but, at the same time, she seems like a real person, and that was important to us. She had to seem like a real girl, who you could've imagined walking home from high school one day and picked [by her kidnapper] just because they're unlucky."
In person, Larson is almost as serious as the film itself.
"I don't take roles that are 'just another role'," she says. "I'm interested in learning more about myself and about humanity. So it should change you by the time it's done."
She calls playing Ma an "emotional marathon" - a race that began long before the shoot. Larson spoke to nutritionists and lost weight until she had just 12 per cent body fat and stayed out of the sun for months to replicate the effects on the skin of incarceration.
Why, though, has Room been hitting a nerve with audiences?
"I think seeing the love between a mother and child is something we can all really relate to," she says. "You can remember it from your own childhood perspective. You can see it from the adult perspective, and see the beauty of where the two meet and where they don't see things the same way, and the importance of growing up and those difficult moments where you have to grow up before you feel like you're ready."
What is remarkable about Room is just how Ma, seven years into her ordeal, is given strength by her love for her son Jack, despite facing the most horrific of situations with her barely glimpsed captor.
"The backdrop to the film is nightly rape, but I didn't want that to be what we see," says Donoghue, who adapted her own novel, itself loosely inspired by the case of Josef Fritzl - the Austrian father now serving life imprisonment for locking his daughter Elizabeth in a cellar for 24 years, raping her repeatedly and spawning seven children.
Larson spent weeks preparing with newcomer Jacob Tremblay, who plays Jack. Each day, they'd sit and quietly bond. They'd draw portraits of each other and build crafts and home-made toys from foil, string, crayons and tape - the sort of basic materials Ma and Jack would have access too - and then take them into "room", as they termed it.
"It wasn't just a set," says Larson. "It had a life to it that Jacob and I had created together."
To keep the mood light, they'd dance together to the Mark Ronson hit Uptown Funk.
"It was very important that she bonded with whichever kid we cast," says Abrahamson, who only auditioned three actresses for the role, despite the clamour from stars to be seen for the part. "She would have to be my right-hand person in bringing this child through this long, arduous shooting process. I needed somebody warm and somebody that a little boy would fall in love with, and that was clearly the case with Brie."
The role opened Larson up like a wound.
"It wasn't the depression of Ma's story," she says. "It was how little I knew of the struggle of being a mother - how the capacity to love is so big. I was able to relive my childhood from my mom's perspective and see how she protected me in ways I never noticed."
When Larson was seven, her mother took her and her younger sister Milaine to Los Angeles for a pilot season to see if her would-be actress daughter had what it took. Her mother installed her children in a studio apartment. This was Larson's own "room", she says. Despite just having the bare essentials - no toys, thrift-store clothes and a junk-food diet - it became their universe. "My mom created this amazing world," she says.
Their adventure was supposed to last only three weeks, but, as it turned out, they never went back to Sacramento. Shortly before the trip, Larson's father had asked her mother for a divorce - something Larson did not realise until years later. She can still recall her mother waking up sobbing, but when Larson began to shoot Room, it was she who was left in tears: "The times that I would cry were when I would call my mom asking for forgiveness for all that I didn't know as a kid."
Even now, Larson is not your sunshine starlet, desperately chasing fame.
"I'm kind of a morbid person," she says. "I'm very optimistic, but I also feel like I'm going to die at any moment. I feel very much aware of my mortality. I'm here and then I'm not. It's the same thing with everything else: the movie comes out and then it's gone. Everything is changing all the time, and I'm not going to stress out and spend my entire time chasing something that ultimately doesn't exist."
Yet Larson is capitalising on the spotlight Room is shining on her. This year, she can be seen in Ben Wheatley's Boston-set crime movie Free Fire and Todd Solondz's ensemble piece Wiener-Dog. Then in 2017 comes Kong: Skull Island, a prequel to the classic King Kong that takes us back to the giant ape's mysterious and dangerous habitat. Co-starring Tom Hiddleston in what will be Larson's first blockbuster, she sees it as no different to Room, with its mythology-alluding narrative.
Touching on everything from Rapunzel to the Ancient Greek myth of Demeter and her daughter Persephone, Room, Larson concedes, will not reach a mass audience in the way that Kong: Skull Island can.
"But that has the same mythological roots," she says. "And although it might seem like a stretch for me to say that, it comes from the same place as Room. That's why something like Star Wars holds such a place in our hearts - a fun, accessible adventure movie that has all of the old mythology in it."
So could Room be this year's surprise Oscar winner? Donoghue believes the groundswell of support that's building is crucial.
"Room is a film that needs this awards buzz because it helps reassure people that it's a film worth watching," she says. "Award talk is like fairy dust: if people are feeling nervous about a film, talk about awards reassures them and makes them have some positive associations."
Much of this is down to Larson and she has already ousted the likes of Carol stars Cate Blanchett and Rooney Mara to pick up her Golden Globe.
The film has scored a remarkable 97% on the Rotten Tomatoes website, aggregating critics' scores - a much-needed boost, says Abrahamson, for a film about a kidnap victim and her child.
"From the outside, imagining this project, you can think this is going to be a tough film because, once people hear where some of it takes place, they think 'do I want to go there?'" he says. "We always felt the film would be life-affirming and that instinct is vindicated by the response of audiences."
Larson once found the red-carpet duties that come with awards shows difficult, until she looked at wearing designer clothes as simply becoming another character.
"Once I was able to embrace that on the red carpet, then it became really fun," she says. "I can be whoever I want. I can feel however I want."
Come Oscar-time, she might just feel like a winner.