THE BROTHEL DOWNSTAIRS from my Shanghai apartment, like so many similar establishments across China, masqueraded as a foot massage parlor. But only the densest or most desperate massage seeker would have mistaken it for a purveyor of the painful rubdowns prescribed in traditional Chinese medicine. Most nights young women in short shorts and exaggerated makeup lounged in the massage chairs in varying degrees of boredom, and the space was lit in pink. The imprint of a foot on the placard outside was about all that kept up the ruse.

As far as neighbors went, the sex workers were fine — quiet, courteous, not prone to cooking stinky tofu. The few times my clothes fell from the bamboo poles used to dry laundry in China, they saved the garments for me until I could make the trek downstairs to retrieve them. We didn’t share an entrance, though a window in the back of the parlor opened onto my stairwell, and on my way home on hot nights I would see the women brushing their teeth. (Even the room that doubled as a kitchen and bathroom glowed fuchsia.) As the years passed I rarely had reason to think about the brothel. But it remained a difficult thing to explain to overseas guests, invariably evoking one of those questions about China that evade any quick, pat answer.

By many accounts, China is in the throes of a sexual revolution, its people having shed the bonds of repressive Confucian values for a period of remarkable openness. If headlines from North American newspapers are any guide, this shift started sometime in the 1980s and then took off with an intensity reminiscent of the Summer of Love. “The Sexual Revolution Isn’t Welcome In China” (1981) became, just a decade later, “Sexual Revolution Dawning in China,” and by 2010, “18 Orgies Later, Chinese Swinger Gets Prison Bed.” The result, as a recent Canadian Broadcasting Corporation documentary quipped, is “China’s version of the 1960s revolution — on steroids.”

And yet, even as the Chinese government lets brothels and sex stores proliferate, it continues to wage its decades-long war against pornography and obscenity. Gay and lesbian groups may be largely left alone now, but their members tend to remain closeted with family and friends, a good portion of them in heterosexual marriages. Even as many more young Chinese have premarital sex, traditional ideas die hard. A commentator in the Chinese press recently compared sleeping with an experienced woman to “eating a delicious meal with a secondhand pair of chopsticks.” Every year thousands of women shell out money to get their hymens stitched up ahead of their wedding day — or, if they’re on a budget, insert an artificial hymen that releases fake blood during penetration.

Richard Burger neatly navigates these contradictions in Behind the Red Door: Sex in China, showing how lust and prudishness, openness and repression, indecency and modesty can coexist in the People’s Re...