I’m in the bedding department of the hulking Tokyu department store, or depaato in Japanese, which sits above the even more hulking Shibuya train starion in central Tokyo. Imagine Bloomingdale’s set atop Grand Central Station.

As I noodle around the stacks of pastel-colored futons, a chubby salesman approaches. He’s wearing a black apron embroidered with the English words Home Show. To my delight, he has studied in New Zealand and speaks a cheerful if halting English.

I point out something that’s obvious to the bedding salesman, who by now has told me that his name is Toru: There are only one-person futons available. The store also keeps Western-style beds in stock, he tells me, but those, too, are only in single sizes (what we Americans call “twin” beds and use mostly for children).

But wouldn’t doubles come in handy? Doesn’t anybody snuggle to sleep in this country?

Toru furrows his brow and lowers his head, in that distinctively Japanese gesture that suggests, “I’m sorry, I’m about to deliver information that will displease you.” Double beds are by special order only, he says, but, as far as he knows, no Japanese person has ever ordered one. The only buyers have been foreigners like me. “They are all working at the embassy or something,” he ventures.

Japan is the land of the single bed. Maybe Japanese couples push their futons together. Maybe they crawl into each other’s single beds the way my grandparents did. But what they don’t do, obviously, is share a mattress.

Is this significant? I’m wary of fetishizing Japan’s sexual habits, as foreigners often do. I had seen that when I studied Japanese for three years and spent a semester of college in Osaka. Back then I even had a Japanese boyfriend named Yuji, who wore a cowboy hat and loved it that my name rhymed with “camera.” Unfortunately for the purposes of my current research, Yuji wasn’t married at the time. And there don’t seem to be any national sex statistics.

I set up a manic schedule of interviews in Japan, arranging to speak to lots of ordinary people and sit down with experts from the government and with leading sociologists and academics. I make appointments with divorce lawyers and psychologists, and hire research assistants to search for statistics and articles about affairs.

I intend to get to the bottom of the mystery of the single futon, even if I have to burst into Japanese bedrooms. Are couples here having regular sex with each other? Are they celibate? Or are they, as I suspect, off shagging other people?

I set out with a novice interpreter named Maiko, who, despite the fact that she gets the giggles whenever anyone mentions sex, charges the egregious fee of twenty dollars an hour. Our first appointment is with a “marriage adviser,” whose office is in a tiny Tokyo neighborhood where trees droop over low wooden fences. I imagine the kids inside the sprawling houses here rushing to the door when their fathers arrive home holding briefcases and shouting “Tadaima!“-the greeting that means literally “I’ve come back!”

When we arrive for our appointment, Maiko and I put on slippers and enter a hygienically clean room to meet Hiromi Ikeuchi. Ikeuchi is a cheerful, petite woman in her mid-forties with a perfectly tousled bob and a fresh coat of red lipstick. Within minutes she tells us that she’s divorced. This is, in fact, her calling card. “I like divorce! I love divorce!” she says. It turns out that her specialty is divorce, not marriage. The pamphlet she hands us explains that her office is called the Tokyo Family Lab — Research Section, which explains the quasi-surgical atmosphere.

On a white marker board, she draws a kinship chart showing the Japanese characters for “wife” and “husband” separated by a red line. The husband is the head of the Japanese household, called an ie (rhymes with “eBay”). When a woman marries, she’s appendaged to her husband’s ie, and her status shifts from “woman” to “wife. ” Ikeuchi draws more red arrows showing that the couple’s children are born into their father’s ie while their mother always remains on the other side of the red line.

No one writes love songs about the ie. It has more to do with property and responsibility than love. The ie is the opposite of the American marriage, where couples aspire to communicate and work on “the relationship.” Ikeuchi says some older Japanese husbands don’t even use their wives’ names and instead address them with a crude form of “you.” Even younger couples begin calling each other the Japanese equivalent of “Mother” and “Father” (or the marginally more modern Mama and Papa) after a child is born.

And then there are the single beds: “Mother” typically moves her futon into the baby’s room and sleeps there until he’s five or six (according to tradition, her husband replaces her in the master bedroom with a large stereo system and a flatscreen TV). Even younger couples who think the formal ie system is old-fashioned retain some of its trappings, snuggling be damned.

I tell Ikeuchi that none of this sounds very sexy to me. She agrees. That’s why they call it “sexless marriage,” she says.

Sexless marriage? Isn’t that a contradiction in terms?

Not in Japan, she says. “Sexless marriage” (or the abbreviated “sexress“) describes Japanese couples who either have very little sex or no sex at all, particularly after their first child. It’s a kind of syndrome that afflicts couples as young as their twenties and thirties and can last for years or even forever, usually without the couple ever mentioning the “problem.” Hiromi isn’t sure how many Japanese marriages are sexress, but she suspects the problem is endemic. She blames the ie heads, some of whom take a strange sort of pride in having a chaste marriage. “There are certain men who believe you don’t bring sex and work into the home,” she says.

That solves the first part of the mystery. There’s not much sex at home. But is it happening someplace else? Or have I found a sexual culture without sex?

Excerpted from Lust in Translation: Infidelity from Tokyo to Tennessee by Pamela Druckerman. Reprinted by arrangement with Penguin Books, a member of Penguin Group (USA), Inc. Copyright (c) March, 2008.

Author Pamela Druckerman is a former staff reporter for the Wall Street Journal. She has a master’s degree in international affairs from Columbia University and has reported from São Paulo, Buenos Aires, Jerusalem, Paris, and New York. She lives in Paris.