Undercover investigator Daniel Walker spent four years infiltrating the multibillion-dollar sex trafficking industry. His account of that work, and the candid story of his own spiritual journey during that time and since, is the subject of a powerful new book, God in a Brothel: An Undercover Journey into Sex Trafficking and Rescue. As he takes you into the very heart of the brothels, the communities and the corrupt systems that profit from and perpetuate human trafficking, Walker reveals an unimaginable horror and appeals to us—and the Church especially—to take on this cause and help set thousands of young women, girls and boys, free from lives of enforced slavery.

Walker answered some questions for us about his work and his story. (For more conversation on God in a Brothel, visit the Patheos Book Club.)

What exactly, is sex trafficking, and how prevalent is it today?

Sex trafficking is very simply coercion and deception. Trafficking is a form of modern-day slavery whereby deception is used initially to deceive or lie to the victim and once they're brought to a particular destination—sometimes that's across the country or across international borders to another country entirely—then the coercion kicks in and in many cases they're imprisoned or told they have a debt to pay before they can go free.

It's estimated that there are approximately 30 million people enslaved in some form around the globe, and that in fact there are more people in slavery in our generation than any other time in human history. Many millions of those are in the commercial sex industry, which earns organized crime more than 32 billion dollars a year. And many of those are inside the United States. There are approximately 2 million children around the world who are sold every day as part of the global sex industry and 100,000 of those are inside the continental U.S.

What do you wish more people knew about the sex trafficking industry?

How huge it is, how prevalent it is, how many people it enslaves and how it is present in their own back yards.

I don't suppose that as a boy you thought, I'm going to grow up and become a sex trafficking investigator. How did you decide to go into this dangerous and difficult field?

As a new Christian at age 17, I was participating in the World Vision 40 Hour Famine to raise money for children who sell themselves on the streets to survive. As I read about these 13 year old girls I realized that my little sister was only 13 years old and I prayed a dangerous prayer; God if you can ever use me to set these children free, here I am.

What did your work entail as an undercover investigator? Where did your work take you?

Posing as a sex tourist or pedophile in Go-Go bars and brothels around the world in more than a dozen countries, including the U.S.

You speak of a transforming moment near the beginning of the book where you move from seeing only the evil in the brothels to actually experiencing God in the brothel. Can you say a little more about that experience?

I was afraid of my sin, the bad guys with guns and evil itself. But as I held this 15-year-old girl on the dance floor of a brothel, and prayed, everything changed. I suddenly saw her not as a threat to my professionalism or purity, but as a child in whose life evil had been allowed to flourish and consume. And I was filled with holy hatred for evil and anger at an indifferent world.