PHILADELPHIA -- If Rachel Weisz has a favorite film genre, it's the one that "Silkwood" and "Erin Brockovich" can be filed under: "You know," she explains, "a thriller in which an ordinary woman does an extraordinary thing, one lone person up against a huge organization, David-versus-Goliath-style."

And that, in a nutshell, is what Weisz, as real-life former Nebraska cop Kathryn Bolkovac, is doing in "The Whistleblower," a tough tale of sex trafficking, corruption and cover-ups set in postwar Bosnia.

Weisz first read "The Whistleblower" screenplay five years ago, and was moved. Bolkovac, a police inspector in Lincoln, Neb., had taken a job as a peacekeeper in 1999 in Bosnia, where she discovered that young women were being forced into prostitution, beaten, abused, held captive, at risk for their lives. She reported her discovery to local officials, to U.N. officials, to anyone who would listen. There were expressions of concern, resolutions made, but nothing was done. In fact, she soon found out that some of her fellow peacekeepers were involved in the sex-slavery ring.

The higher up the command chain she went, the less welcome she became.

"I was actually pregnant at the time that I first read the script," Weisz recalls. "I just thought it was the most astonishing piece of writing, and the most astonishing true story. But I couldn't quite cope with it at that moment.

"And then, I think when my son was about 2, I remembered it -- and I called the producer and asked if the script was still available. ... It stayed with me. There was something about it that I couldn't forget."

Filmed in Bucharest, Romania, last year, and costarring David Strathairn, Monica Bellucci and Benedict Cumberbatch, "The Whistleblower" was made for far less money than your typical international thriller.

"We shot it in just under six weeks," says the English actress, who sports an American accent and a steely demeanor in the film. "Most thrillers would take three months or so."

Another actor of note that Weisz shared screen time with on the project was Vanessa Redgrave, who plays a U.N. human-rights commissioner. Redgrave is forceful, elegant, precise.

"I had never met her before," Weisz says. "It was a great thing to get to do some scenes with her. She's quite something. A powerful lady ... pretty bold. I asked her if she'd ever been asked to be a spy, and she said, 'I can't possibly answer that." '

Speaking of spies, Weisz, who was just wed to Britain's most famous spy, James Bond, er, Daniel Craig, has been on an espionage and international-intrigue jag of late. She has already filmed "Page Eight," an MI5 drama from writer/director David Hare, with Ralph Fiennes, Bill Nighy and Felicity Jones. And next month, she starts work on "The Bourne Legacy," the post-Matt Damon "Bourne" sequel, to be helmed by Tony Gilroy, with Jeremy Renner, Edward Norton, Joan Allen and Albert Finney.