Dianna Agron's career has thus far placed her so firmly in the high-school experience that sometimes it's easy to forget that she's not actually a teenager at all, but 27 years old. "I am, a bit of a woman now, I'd like to think," she jokes, putting on a mock-cockney accent. It's a gentle reminder and a timely one. Mainstream audiences know her best as Quinn Fabray, the pert, acid-tongued cheerleader, and teen mom from Glee. Now, in her most high-profile role since leaving the show, she's back in school, though this time in France. She's the young daughter of an ex-mobster (played by Robert De Niro) and his glamorous moll wife (Michelle Pfeiffer) struggling to adapt to her new surroundings in Normandy, to where the family have moved incognito while under the witness protection programme.
It's a high-camp, ultra-violent farce, juxtaposing the family's day-to-day trials and tribulations with their propensity to overcome whatever stands in their way by dishing out savage beatings and cold-blooded murders. Agron is one of the best things in the film – she plays Belle Blake, a sexy young psychopath, dangerously in the grip of her first love.
She successfully grounds the more preposterous aspects of the plot in concrete detail. For this, it helps that there are parts of Belle's experience that she can relate to directly. Being the new girl, for a start. Agron was born in Georgia, but when she was growing up, her father worked as a hotel manager and the family moved around a bit.
"When I moved to San Francisco I was nine," she says, curled up against the cold in an oversized coat, and clutching a cup of herbal tea. "And I remember, when I'd been living in San Antonio, at break, you would go and play sports with all the boys. So I remember at recess going up to the other girls and being like, do you play basketball and soccer? And they were all looking at me like I was an alien. With the BOYS? I think one girl was actually doing her nails, they were the most sophisticated young people ever. And I thought it was so strange."
Though Quinn Fabray is firmly part of the in-crowd, that wasn't always the case for Agron. Though her wholesome good looks must surely have set her out for top-table credibility in the cafeteria.
"Slowly by the end of the year, I'd become friends with the girls, and more people – there would be girls that would go play basketball or go play soccer and I remember feeling like such an outsider at first, but breaking through that wasn't that hard in San Francisco. But I was teased a lot in Texas. I was Jewish and that was strange to people."
Still, by the end of high school she was homecoming queen. Though by the sounds of things, she was more naive, less precocious and knowing than one would imagine of a school queen bee. "I was on the homecoming court, junior and senior year. But it wasn't because I was cool. It appears that way, especially because of what we see in movies or whatever, but by that point, people would vote for who they liked, and both my friend Laurel and I would tie each year, because we were really involved in school and we were nice.
"Sometimes when you look at my high school experience in pictures, that picture – you can be like, well clearly you were so popular. Well, not really. And I had so many horribly embarrassing things that happened to me."
In fact, by the sounds of things, she was quite sheltered growing up. For one thing, her mother didn't let her watch any contemporary TV or films, which must have been quite a significant point of difference with her friends.
"I was watching all these old musicals, and I Love Lucy," she says.
Why, I wonder, the ban on modern pop culture? "I was the oldest child and things that she didn't know, she was afraid of showing me," Agron says. "Those were the movies she grew up with, so she knew there was a certain amount of loveliness to those movies and she could trust them, I guess. With my brother it was out the window. My first PG13 movie was when I was 14. My brother did karate so he was allowed to watch this R-rated [under 17s accompanied] karate film, I was, like, this makes no sense. He is 10. And they were like, yeah, but it's karate."
In the end, she thinks it worked out pretty well for her development as a performer.
"The people that I loved the most were Audrey Hepburn, Lucille Ball, Leslie Caron and Sophia Loren. It was a very specific style back then, and it did feel like such a fairytale to be involved in movies, particularly when they were so fantastical. You watch them and it's just a different era. I think that was very helpful to me and why I wanted to pursue it."
In The Family, Belle falls hard for her maths tutor, and is pitched into hormonal despair when he ends their romance. I wonder if homecoming queen Agron ever went through that adolescent rite of passage herself?
"I definitely have a friend who was just the best boy in the world – the coolest boy in the world. We didn't really date so much as become best friends, and he was definitely my first love. And we're still friends today. And then of course I decided to date this guy who completely broke my heart and cheated on me. And so I was, like, I'm going to move to LA and I'm going to focus on my career. There were no boys holding me back in San Francisco."
If success is the best revenge, Agron seems to be doing well at getting hers. She's the first of the core cast-members of Glee – the show that launched a new generation of all singing, all dancing stars – to have cut out on her own, making the transition to the big screen. Glee, she says, was the perfect launchpad. "With those people it was the perfect mix of everything I needed to prepare me for everything else. We cut our teeth on that show, and it's always going to be so special because of that."
The cast of Glee has always loudly advertised the closeness and friendship between them. But after the male lead, Cory Monteith, died of a drug overdose earlier this year, darker rumours were sparked. Dianna wasn't part of the high-profile tribute episode of the show written and performed in Monteith's memory, which aired last month, and suggestions of a bitter rift between her and the other cast members began to circulate online. But she wants to put the record straight,
"Bad news spreads faster than anything good. And I think it's just such a shame, especially involving someone that we love so much, that the good old internet has taken everything that they want to say about it and spread it like wildfire," she says, sounding genuinely hurt.
"So I've nothing but love for that show and everybody involved in it and it was such a huge part of my life, so I think it's equally hard when I'm not there every day anymore, I don't see all of them every day anymore to have things like this fly around. It's more heartbreaking than it would be if I was there with everybody. It makes me feel even farther away from our show."
The Family is in cinemas from Friday