BOX ELDER County, in the far north-west corner of Utah, above the Great Salt Lake, is only sparsely populated. But it gets its share of crime. When the telephone started ringing in the county sheriff's office at 3am three Sundays ago it was a fair bet someone out there was in trouble.

With a broken nose and her legs and arms swollen with bruises, a 16-year- old girl had struggled seven miles to a petrol station to find a telephone. She had been beaten and abandoned by her father, she said. But the girl began to fill in the details only reluctantly, and after hours of interviews at the sheriff's office. After driving 90 miles from their home south of Salt Lake City, her father had taken her to a remote barn. He had punched her repeatedly and whipped her about 20 times with a leather belt.

Then she gave her father's name. The police knew it. It was John Daniel Kingston, patriarch of one the largest polygamist clans in Utah. The girl said he had attacked her because she did not want to be the 15th wife of his brother, whom she had been forced to marry after her 16th birthday. The beating was meant as punishment after she had run away from her husband/uncle for a second time.

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"She didn't want to pursue charges and she didn't want to give us any names," explained Detective Scott Cosgrave, head of the investigation. "All she wanted was to be allowed to lead a normal life for a 16-year- old: go to school and not be the 15th wife of a man she doesn't want to be married to."

Finally, though, she agreed that charges could be pressed. Last Tuesday, hours before a court-set deadline, Mr Kingston surrendered to the sheriff and was released on $10,000 bail. Later this week, he will appear in court to be formally charged with child abuse.

His trial, however, will be about much more. It promises to lift the lid on Utah's most awkward secret. Polygamy, imported into the state by Mormon pioneers 150 years ago, is alive and well.

We know little about Utah's polygamists because no one wants to talk about them. They are an anathema to the mainstream Mormon Church, formerly the Church of Jesus Christ of Latterday Saints, which banned polygamy in 1904 and dissociates itself from the fundamentalist Mormons still practising it.

Likewise, polygamists represent an acute embarrassment to a state that will stage the Winter Olympics in 2002 and which cultivates an image of prosperity and modernity. According to some experts, polygamy is still practised by 50,000 to 60,000 fundamentalists in Utah. While it is technically against the law, the authorities have preferred not to prosecute, opting always to turn a very deliberate blind eye.

There are other reasons for the reluctance. Polygamous families are secretive and self-reliant, perhaps paranoid, and skilled at deflecting outsiders, police investigators especially. "They don't like the spotlight and they don't like attention," Det Cosgrove said. "They make it very difficult for us, giving us phoney addresses and things like that. Basically, they want us to believe they don't exist."

Polygamist men, who sometimes have 20 wives or more, have circumvented the law by registering only the first of their marriages with the civil authorities. Their subsequent marriages are conducted in secret. Moreover, any attempt to enforce the law and to disband plural families would hit delicate constitutional issues likely to go all the way to the Supreme Court.

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With the Kingston incident, however, the authorities suddenly found themselves not only with an opportunity to start turning over the polygamist stone, but an obligation to do so. The case, after all, is about abuse. Abuse of women is what most of us think about in connection with polygamy. That and sex.

"I'll tell you what polygamy is in a nutshell: it's one big eternal fuck in the name of God," spat Roweena Erickson last week. "No more, no less."

Ms Erickson, 58, should know. In 1994, she fled the Kingston clan with eight children after 34 years of marriage to Leon Kingston, son of the group's founder and a cousin of John Daniel. Leon still has one other wife, Roweena's elder sister. For four years, she has been trying to get someone, anyone, to listen to her story and to take action against the Kingstons. Last week, she told it to The Independent.

The picture painted by Ms Erickson confirms our deepest suspicions. Child molestation, kinky sex, pornography and incest all feature. So do genetic disorders. The clans, Ms Erickson says, have high rates of dwarfism and macrocephalous (enlarged) heads. She adds also organised crime, violence, extortion and even murder.

"It's a bad, sick cult and they're sexually deviant. Mothers will give the wives of their sons vibrators, because they know their sons will not always be there for them. They make porno movies. The wives perform deviant sexual acts with the children. I heard of a father who does his son's impregnating because his son is sterile."

Believed to have business assets worth at least $150m, the Kingstons, according to Det Cosgrove, have been under scrutiny by federal law enforcement agencies for some time. Illegal gambling, for example, is suspected. But Ms Erickson believes there is more. "I saw the illegal activities going on, I had heard rumours that they had mafia connections, which I believe they do, and I had heard that they had had people bumped off. And I believe they are laundering money for the `Mormon Mafia' in Las Vegas".

It took years for Ms Erickson to realise that her religious beliefs, which included the notion that polygamy was a prerequisite for the attainment of eternal celestial bliss - was not enough to sustain her. "I was thinking, if this is so wonderful, why do I feel so horrible? Why is my gut telling me something is amiss?" Finally, she went and told Leon: "I'm not living this god-damned fuck-up polygamy any more." And she left.

Public relations is not a skill widely held by polygamists. But, conscious of the bad publicity from the Kingston case, Bart Malstrom, the husband of four wives and 12 children, agreed to talk. On rainy afternoon in Fairview, two hours south of Salt Lake, Bart, 39, Pam, 38, Wendy, 33, Monique, 27, and Nicole, 23, (these last two are also sisters) gathered in the living room in one of their three houses clustered together to explain the joy of their life.

On the face of it, it was a convincing display. The children, ranging in age from seven months to 17 years, made the occasional appearance.

The family survives by manufacturing and marketing a herbal, medicinal tincture and growing their own vegetables. Their church, one of many splinter fundamentalist Mormon churches that still encourages polygamy, is called the "True and Living Church of Jesus Christ of Last Day Saints".

"It's a sad thing any time that a father would abuse any child," offered Bart, an imposing figure at 6ft4in, in a sweat-shirt bearing the slogan: "Help us to Stamp Out Monogamy". "Because this one happens to be a polygamous, it hits the papers a little bit harder. But child abuse is not anything out of the ordinary in the society we live in. The fact that it was in a plural marriage has got nothing to do with it."

Pam sees hypocrisy and double standards in our fear of polygamy. "People accept so many different lifestyles today; people living together, male with male, female with female, everyone going to bed with whomever they want, but they can't accept plural marriage."

It is Monique, perhaps the most reticent of the wives, who explodes at the notion that anyone would attempt to break up their apparently happy fivesome. "This is our family. He is the father of our children, he's our husband, this is our family. We have nowhere else to go We take care of our needs, we don't bother anybody. If you met one of us on the street you wouldn't even know we were polygamist." True enough.

None of this will impress Ms Erickson, who, with two friends, is setting up a support group in Salt Lake City for women looking to escape from polygamous situations. They have named it Tapestry of Polygamy.

With all the publicity from Box Elder County, she hopes her own story will at last get some attention. Might the evil she sees at the heart of the Kingston clan finally be extinguished? The prospect is too sweet for her to put into words. Tears welling up, she simply leans back and crosses fingers on both hands.