The turning point? "Joe said in public that he was waiting for the annulment to come through to get married to Beth. . ." Bad call. One presumptuous remark, and four years later Joe Kennedy still has no annulment, has seen Kennedy Catholic values mercilessly exposed, has brought himself and the US church into public disrepute and seen an end to his hopes of being elected Governor of Massachusetts.

It is the presumption of it that shocks. The presumption that his first wife Sheila Rauch (pronounced "Ouch") would roll over and pretend that their 12-year marriage never existed; that the powerful Kennedy-church alliance could silence all dissenters in any event - after all, as he often reminded her, in Boston she was a "nobody"; that he could marry his secretary, Beth Kelly, in a full, Catholic wedding with no questions asked - not least by his own twin sons, the 12-year-old offspring of a marriage he was now prepared to swear never really happened.

Still, to him, the omens must have seemed good to begin with. It was Sheila after all, who had first recognised that the marriage was beyond salvage and filed for divorce; Sheila who wasn't even a Catholic (she was Episcopalian and remains so); Sheila who had left the family home with what must have been a crashing sigh of relief. So why wouldn't she agree to do this one little thing for him? It's a question she has been asked on many occasions since. And to her credit, she affects no mock outrage at the idea. In fact, it is her cool reserve that marks any interview.

But her reaction to the first notification that Joe was intent on annulling their marriage was dramatic. She - who prided herself on a strong stomach - rushed to the bathroom and vomited, while concluding that Joe "must simply be out of his mind". They had known each other for nine years before their wedding and been married for close to 13.

"I could not go along with him on this. Marriage, even one that was over, remained a sacred bond. Though divorced, I remained loyal to it. Now by denying the sanctity of our marriage, Joe had broken that bond. I could not back down and face either myself or my children." There was a vast difference, she believed, between a valid marriage that had gone sour and one that never existed. Joe's response was a mixture of anger and disbelief. "How can you be opposed? What right do you have to be opposed? How can you prevent me from going on with my life?"

By the end of the conversation, she had learned two things.

One, that though Joe believed their marriage had indeed been perfectly valid, this was no obstacle to his plan: "I don't believe this stuff (that the marriage had not been valid). Nobody actually believes it. It's just Catholic gobbledegook, Sheila. But you just have to say it this way well, because that's the way the church is."

And two, that he was utterly confident that he would get the annulment in spite of her. For all that it was "gobbledegook", the grounds on which he sought the annulment were "lack of due discretion of judgment" - on her part, not his. In other words, Joe and the Boston archdiocese, his willing little helper, were setting out to prove that she was "crazy" when she married him in 1979.

Nothing about Sheila Rauch Kennedy suggests that she was ever remotely crazy, even for a moment, or prone to impulsive behaviour. Episcopalians are the upperclass, blue-bloods of the US - a fact which may explain her appeal to a Kennedy. "They call us the `Frozen People'," she responds with a small smile when I comment on her exasperating restraint. Neither is there anything crazy about the book or its subject. In fact, for anyone seeking dirt on the Kennedy family, it is gallingly discreet.

Though she was "a little surprised" to hear that Joe was in a relationship with his secretary, she was pragmatic enough to conclude that he "could have done a lot worse. Joe clearly wanted someone there for him, and Beth takes good care of him - and good care of the kids when they're with them." She notes that they have no children: "It's interesting because he wanted more kids - a lot more. She is still his secretary and scheduler and travels with him constantly."

In spite of Rauch's cool exterior, it soon becomes obvious that nothing she says lacks meaning. As a result, when she describes an emotion of any kind, the phrase jumps off the page, as, for example, a sentence relating to her fear of confronting Joe: "I had never faced the truth that by the end of our marriage I had simply become afraid of him."

Afraid? - this handsome, strong, talented woman? Did she mean he was violent towards her? A long pause, apparently for careful consideration (although she has been asked this question before). Was he?

"Joe is the first to admit that he's got a temper. But no. . . (pause). . . not directly violent to me. He does have a temper. . . " How, then, did it manifest itself?

"Well, it was always there but even more once he got involved in politics, because as a Kennedy, people fawned over him constantly. . . Then he'd come home and I'd be raising the kids and the kids had to go to soccer, the garbage had to be taken out, homework to be supervised, there were a lot of things to be done, life had to continue, and I wasn't prepared to fawn. I could never make the adjustment from what it had been like before. . . "Anyway, he would come home from Washington and would be very, very demanding. I would be there keeping things going - for example, we had two houses at one point because we still had the first house after we moved and there were animals still down there that I had to drive down and care for on top of all the other things - but he would still come in and - oh, it might be something like, he'd open the refrigerator and find two creams (an American soft drink) instead of three or that I'd got English Breakfast Tea instead of Irish Breakfast Tea. . . "

Joe, by implication, is a rough, tough man; wonderful if he's on your side and the situation calls for bared-teeth tenacity, formidable if he's not. By all accounts, he prides himself on this: "He has referred to himself as the `family pitbull'," she says with a rare smile.

The change from reasonable, loving husband, she recalls, was sudden and coincided with his entry into politics. "It was almost worse during the campaigns because then the fawning was 24 hours a day, everywhere he went, and of course the campaigns go on for years." But had she not anticipated that - not seen how the Kennedy women before her had resigned themselves to the ghastly burden of political wife?

"Yes, political wives took that burden seriously - `the quiet sufferer'," she quotes wryly. "But we were another generation. Even if I wanted to live like the Kennedy women, I couldn't. We didn't have cooks and nannies. It's the great duality, isn't it? In one sense, we're supposed to be modern enough to take over and do everything ourselves; but in another, we're expected to remain in the role of the old-fashioned, submissive wife. . ."

Again, financial issues between them are not dealt with directly in the book but there are plenty of signals, indicative either of a stubborn independence on her part or a lack of generosity on his. But the perception of the Kennedys is of cooks and nannies, wealth and glamour, I suggested. . .

Again a long silence. Then finally: "I never got that message." Clearly, money is still tight. A demand from the archdiocese for $850 to appeal her case to Rome (three times more than it cost Joe to procure the annulment) was met with objections not only on principle but also that she simply didn't have the money: "The holidays were coming and I certainly didn't have an extra $850 to send to the tribunal."

Although there was no prenuptial agreement, she did not ask for alimony. When they separated, she moved out of the house and borrowed money from her parents to set up a new household for herself and their children. And, she writes: "I stayed in Massachusetts to facilitate his visiting the boys, and perhaps most important for someone with political ambitions, I kept quiet." Until she saw the report that he was "waiting for an annulment to come through" to marry Beth. He had crossed the line.

The statement provoked "national though superficial press coverage of what I considered to be the serious issue of our marriage and its implications for our children". She chose to respond to an article in Time magazine. Her friends were startled; it seemed very out of character for the Sheila Rauch they knew. It was. But the struggle was changing her - forcing her to defend the validity of her marriage for her own and her children's sake, and in the process to cast off her old fear of Joe.

The first of many hundreds of letters she received was from Deirdre, an Irishwoman of farming stock who had emigrated to the US with her husband and small daughters in the early 1970s. She too had seen her marriage annulled on the grounds of "lack of due discretion" - despite a three-year courtship, a wedding of two mature adults (he was 31), 26 years of marriage and three children.

As in many other cases that have come to light through Sheila Rauch's research, opposition meant little. The tribunal would allow Deirdre to review "some" of the testimony: "But how can one refute testimony one is not privy to? What if the testimony one doesn't see is the testimony on which the tribunal bases its decision?"

Deirdre got the news of the annulment second hand - through her daughter, tears streaming down her face, after hearing it from her father. A "typing backlog", said the tribunal, explaining why the ex-husband, a doctor, had got to hear of it first. The annulment was granted on the grounds of his "lack of due discretion" - but this lack of discretion failed to preclude him being remarried eight weeks later with the full blessing of the Catholic church.

As more and more women came forward with their stories, it became apparent that it was by no means rare for middle-aged men to receive annulments and remarry in the church. "The general impression seemed to be that annulments were being handed out like candy." The awful irony for many of these women is that they had been pillars of Catholic parish life, following orthodox teaching on birth control at great personal cost, living the full Catholic vision of full-time mother and support for the husband.

"From what women have said," says Sheila Rauch, "the church made them believe that their whole lives were in being wives and mothers. Then when they're too old to bear any more children and their marriages fall apart, the church tells them they were never really married in the first place. The man they thought was their husband often remarries a younger woman who is more likely to have children, and the church blesses the second union. "In a religious sense, it's sort of like sending the brood mare to the glue factory when she can't have any more foals. Actually, in some ways it's worse. No one ever said the brood mare didn't exist, but that's what the church is saying about the marriage when marriage was those women's lives."

The Catholic church in the US grants over 50,000 annulments a year. Joe Kennedy (already remarried in a civil ceremony) did get his annulment from the Boston archdiocese; the latter's facility for Machiavellian contortions may be gauged from the fact that it was obliged to turn the original indictment on its head and accuse him of "lack of due discretion" to get a "positive" result. Sheila Rauch is appealing the decision to Rome. This could take up to seven or eight years.

Rauch's history of her own annulment process and the church's attitude down through history makes startling and infuriating reading. Meanwhile, the US church continues to "market" annulments to entice divorced Catholics back to its fold. But the price, as outlined in Rauch's book, is enormous; the thousands of distraught, bewildered and disaffected women and children which the policy of "compassion" is leaving in its wake.

Shattered Faith by Sheila Rauch Kennedy is published by Poolbeg, £7.99 paperback.