When Kathryn Bolkovac went to work for the UN peacekeeping mission in post-war Bosnia in the late 1990s, she was horrified to discover a thriving sex-trafficking trade.
But what was even more shocking was that some of her colleagues were involved.
When she tried to expose the abuse, she was fired by her employer, the private military contractor Dyncorp. She eventually won a case against them.
Now her story has been made into a major Hollywood film, The Whistleblower. She's also just written a book about her experience. Kathy Harcombe went to meet her.