At the beginning of Jason Bourne, her fourth film in the blockbuster action franchise, Julia Stiles appears in near-total darkness.
"Christian Dassault sent me," she says in a voice so low she could be a man or a woman.
That password admits her to a hackers' headquarters in Iceland. Within minutes, she has broken into the CIA's mainframe and stolen top-secret files, unleashing the action for the rest of the film.
In the nine years since Stiles and Matt Damon last joined forces for a Bourne movie, both their characters have been living "off the grid". The change in Nicky Parsons, who began in 2002 as the neat CIA analyst Nicolette and appears in Paul Greengrass' new film under the hacker codename Knightrider, is dramatic.
Not only has she gone rogue - smart, wild and threatening - but, under cover of a riot in Greece, she lures Bourne out from hiding, in the film's single most impressive sequence.
"It seems a little bit exploitative for me to say this, but I get chills when I think about the scenes that I was in," she says when we meet, early on the day of the British premiere. "Paul Greengrass has a knack for setting an action movie in a world that is very familiar to us.
"He can keep the political issues and the environment very timely and relevant. He wrote it a year ago. But it feels shockingly familiar given all the protests and violence that we've experienced in the United States."
Stiles first read the script of the 2002 film The Bourne Identity - or at least, the parts she was allowed to see - when she was in her dorm room at Columbia University. She was 19, and already enough of a teenage star that going to college was in itself an unusual move.
"I remember thinking Doug Liman was a really interesting director. At that time he was more of an indie darling," she says now. "And I thought it was really intriguing that Matt was going to play this action hero, because at that time he wasn't an obvious choice."
In the first edit, her character died. "She was thrown up against a wall and her neck was snapped," Stiles recalls - but the film was recut to make way for a possible sequel with her in it. As a result, she has lived with Bourne, as she puts it, "my entire adult life".
By the time that script arrived, Stiles had already starred in the magnificently tart teen rendering of The Taming of the Shrew, 10 Things I Hate About You, alongside the young Heath Ledger; she'd been Ophelia to Ethan Hawke's modern-day Hamlet in Michael Almereyda's urban indie film; she'd been cast in State and Main by David Mamet, whose play Oleanna she'd go on to perform on stage in New York and London; and she'd played the lead in Save the Last Dance, an inter-racial teen love story released to distracting levels of success while she was in her first year at Columbia.
This was not long after she'd been deemed by Neil Jordan to be "too old" for the part in Interview with the Vampire that eventually went to a squeaky Kirsten Dunst. Dunst is just one year Stiles' junior. The truth is, though, Stiles would always have been too old for a part like that. She brings to everything she's done a quality of seriousness that is rare in real life and even rarer in Hollywood.
"I remember finding that character very refreshing," Stiles says now of Kat in 10 Things I Hate About You, "because she was so angst-ridden. Or just brassy and more fierce than any other example of a teenage girl I had seen."
Wonderful though that film is, contemptuous teenagers are arguably more familiar fare than adult women with equal levels of severity. So Stiles' exceptional nature has become more emphatic the longer she goes on, and the fewer prisoners she takes. In the Bourne films, she signals a kind of intelligence that genre films don't usually require of their female characters.
A Bond movie wouldn't know what to do with a Stiles in its script. Alicia Vikander, the ostensible heroine of the latest Bourne incarnation, struggles to achieve CIA steeliness, but Stiles is all determination and ticking thought from the moment of her arrival.
In person, she's equally austere. Once rumoured to have dumped a boyfriend because he didn't like the novels of John Steinbeck, Stiles admits now that she's often stopped in the street by men telling her to smile.
When we meet, her replies to my questions are considered, friendly and even unguarded - she volunteers the information that she's just got engaged and is looking forward to "nesting" with her fiance, cameraman Preston J. Cook - yet her face is so still and her gaze so direct it's disarming. You'd call her expression deadpan if she were joking, but she's not.
I ask Stiles if she thinks people are afraid of seriousness in women, and she cites the Bechdel Test, a theory devised by the graphic novelist Alison Bechdel. "She developed this idea that there's a litmus test for movies," Stiles explains. "There've got to be two main female roles, and they have to have a conversation together that's not about men. I can't think of an example of a movie that passes that test."
Some of the more interesting roles for women, she says, can be found on television. Stiles took on the gruelling role of a mother with a secret life as a prostitute in Blue, and she's about to move to the south of France to film Neil Jordan's Sky series, Riviera, in which she plays the widow of a wealthy and corrupt art dealer. "I'm not exactly sure why," she says, "but I feel optimistic".
She has directed a short film, and a more recent short web series, Paloma. Being in an editing room taught her a lot about acting, she suggests, and although she'd like to direct a feature (many years ago, there was a mooted adaptation of Sylvia Plath's novel The Bell Jar), doing Bourne reminded her how much work directing involves.
Meanwhile, she's listening to a lot of music - Nina Simone's covers of protest songs are a current favourite - and for the past year, she's been taking singing lessons. "Not that I'll ever sing in front of anyone," she adds, a note of self-consciousness creeping into her voice. She sings a lot of Patsy Cline, she says, "because I have quite a low voice - but I've been able to expand my range as a result of these lessons".
Though Stiles sometimes travels with what she calls a "baby banjo", she says there's no chance she'll join a band either. "If I could put a mask on, I would, maybe. I guess I'd have to get over being self-conscious."
As for married life, there are no immediate plans for a wedding, she says. "We're in the daydreaming phase, where we fantasise about where it would be, and the food and the music, but we don't actually get around to concrete things." For now, after a lot of travelling between New York and Canada (where Cook is from) or wherever either of them happened to be working, she's just pleased Cook is also getting to work on Riviera.
"It went from me being anxious and terrified of our being separated for a while to now getting to work together in the south of France. It's a pre-honeymoon, I guess." She pauses. "That might make me nervous. But we'll see."
Jason Bourne, the fourth film in the franchise
In cinemas today.
- The Telegraph