She was 49, a recent immigrant and deeply in debt to a loan shark back home in China when she answered an employment ad three years ago that promised thousands of dollars a month, but offered no job description. She realized too late that she had been tricked into working at a massage parlor in Flushing, Queens, where besides kneading backs, she was expected to sexually service up to a dozen men a day.

Some of the clients were violent, and the boss charged $10 a day for her to sleep on a sofa in a room at the parlor where rats nibbled on her food. "The customers were very terrible," said the woman, who, ashamed of the stigma of her former profession, asked that her name not be used. "After you perform a service, they would find an excuse to take the money away." They would, she said, "do even worse things."

In strip malls across the country, neon signs and brightly colored placards promise hot stones, acupuncture and shiatsu with photos of women or couples receiving relaxing shoulder rubs. But a traditionally Asian form of therapeutic relaxation with deep roots in big-city Chinatowns has spun off a different kind of massage parlor that has little to do with traditional remedies. It has exploded into a $3 billion-a-year sex industry that relies on pervasive secrecy, close-knit ownership rings and tens of thousands of mostly foreign women ensnared in a form of modern indentured servitude.

[Read more about a thriving sex trafficking trade in Florida.]