Two years ago, I got off the phone after an interview and cried my eyes out. I'd just spent an hour talking to Tim Ballard, the founder of Operation Underground Railroad, an organization that helps fight child sex trafficking, and I just couldn't take it.

Ballard told me about how the training to go undercover as a child predator nearly broke him. He told me an eerie story of a trafficker who could totally compartmentalize, showing Ballard photos of kids he had for sale, then switching gears to proudly show him a photo of his own daughter on her bicycle, just as any parent would. He told me about how lucrative child trafficking is—how a child can bring in three or four times as much as a female prostitute—and how Americans are the industry's biggest consumers.