The Civil War savagery which resulted in the murder of her fatherand grandfather drove Una O'Higgins O'Malley to a life of relentlesscampaigning for reconciliation. As she celebrates her 75th birthday today,she explains to Kathy Sheridan how she came to forgive the killer of her fatherwho said he had danced on his grave, and shedescribes the shock of finding out the truth about her father'srelationship with Lady Lavery

Una O'Higgins O'Malley turns 75 today and remains elegantly slim and impeccably dressed. In the light-filled Dublin apartment she shares with her husband, Eoin O'Malley, two comfortable chairs sit companionably side by side. Local histories and travel books line the coffee table; on the sideboard stands a playful photograph of two young grand-daughters; on the walls, a Sarah Purser portrait of her lovely mother and a likeable AE painting of children on a rocky shore.

The unwary could under-estimate her. In body and spirit, there is an almost ethereal quality about this woman who has spent her life searching for truth and beauty, forgiveness and healing, in everything, however ugly and destructive.

So gentle is her tone, in fact, that a casual reader of her recently published memoirs could skim through them and come away with a joyful portrait of a charmed upper-middle-class upbringing, filled with gracious houses, dancing classes, children's parties, beautiful women and pretty children; a world where major historical figures were comfortable fixtures in the social circle and that enviable "Clan" - that great, continuing linkage of distinguished, attractive kinsfolk - provided an anchor in good times and bad.

But the unwary should never forget. They might take her to be a soft-centred creature of sheltered privilege with a bee in her bonnet, but her mission is rooted in the blood-soaked spiral of Civil War savagery which resulted in the murders of her father, Kevin O'Higgins, the Free State's Minister for Justice and External Affairs in 1927, and her grandfather before that.

Her mission has been relentless and has involved every tactic, from rain-sodden protests outside Sinn Féin's offices, to co-founding the Glencree Reconciliation Centre, in Co Wicklow, to standing for election to the Dáil as an independent candidate, to harassing no fewer than four successive cardinals and a Pope.

She offers "energy" bars with the cups of tea, and conversation that swings naturally from questioning the present to bringing alive the past.

No one ever spoke to her about forgiveness, she says; it was "imprinted" in her. The men who shot her grandfather in his home for being the father of Kevin O'Higgins were almost certainly neighbours and known to her grandmother. Yet she would never identify them and insisted on forgiveness and no reprisals. Four years later, when Una was five months old, her father was shot on his way to Sunday Mass. During his five conscious hours, he too chose not to identify his killers, speaking only about forgiveness.

Sixty years later, it would be revealed that Kevin - with eight bullets in him - had managed to speak to his assailants on the roadside, telling them that he forgave them, that he understood why they had done it, but that this must be the end of the killings. There was some doubt that this occurred, but later, one of the attackers, Bill Gannon - who told this to his son - would only speak of O'Higgins as a "very misunderstood man" and would no longer carry a gun.

But what of another of the gang, Archie Doyle, who had danced on her father's grave? "I discovered about that while leafing through Uinseann McEoin's book in an airport bookshop in 1987 and I got seized with this awful, awful unforgiving cloud, that I hadn't ever felt as badly before. I couldn't stop it, it was like this lava pouring from a volcano . . . I had so often gone to that grave. That happened on Holy Thursday and I thought 'so much for Holy Thursday and Jesus Christ and all that'. I wanted to throw the whole thing out there and then. But on Good Friday, I made my way back to the church somehow and as I put my foot on the church porch, I had this thought - 'Have a Mass said for them all'. And that was when I felt normal again . . ." And so it happened that 60 years after the murder of Kevin O'Higgins, his daughter arranged a memorial Mass in Booterstown church for him and his killers, including Archie Doyle.

Her forgiveness endured, though there was much to forgive. She missed her father terribly as a child. "It was the not knowing him that was the agony. I yearned for a father who would have been fun and who would have been proud of me the way the father of my friend Ruth was proud of her . . ." Her older sister, Maev (who became a Carmelite nun), dealt with her loss by completely blocking out any memories of him.Their mother, Brigid, became virtually disabled with migraine, brought on, it was said, by the shock of her husband's murder. "It was an ongoing thing, the kind that sucks the life out of a home. I remember thinking that it is almost worse what happened to my mother than my father," says Una.

And yet on her First Communion day, when she was just five years old, Una says she remembers thinking: "You're either for what this is all about, or against it. Or as my father used to say 'either religion is worth nothing or it is worth more than everything'."

Which probably made all the worse the discovery, much later, that her father, this idealised figure, was not above temptation. The confirmation, only in recent years, that he had indeed had an affair with Lady Hazel Lavery in the two or three years up to his death, was a blow.

"That was a major shock. I had always been so positive that there was nothing more to that than friendship - and you wouldn't know with a public figure what stories might be told about him. [Lady Lavery was known to be a bit of a drama queen who was in the habit of showing the letters around, so suggestions she had doctored them to appear more amorous could not be dismissed out of hand\]. But I was convinced when I actually saw his letters to her".

It didn't help that Lavery's biographer, Sinéad McCoole, who discovered the letters, failed to warn the O'Higgins family of what was coming up the tracks.

"I'd have known Sinéad quite well and she would have talked over quite a number of things with me about that period. It's true that she came across the letters after she had last been in my house but she never contacted me to tell me about them and the book was practically in print before I knew."

But there is no rancour. And far from showering abuse on Lady Lavery and her wiles, Una's reaction was to make a public apology on radio to the Lavery family for the hurt caused by suggestions that the woman had fabricated the story.

As for her father, she believes that he was particularly "vulnerable" at the time. "It was about 1924 or '25 when he first became enamoured of Lady Lavery and during those few years, his first home was burned down, he had had to live in government buildings [where her mother Brigid gave birth to Maev\], his best man Rory O'Connor was executed by his government, along with six others, and his father was killed in his own home. There were several quasi raids and attempts to be coped with . . ." And not least, he lost his only son, Finbarr, in 1924, a healthy boy who succumbed at two weeks to pneumonia contracted, it was said, on the day of his baptism. That death was so "grievous" to O'Higgins that he even briefly believed it to be the work of an enemy. Later, Brigid would say that for her, the loss was comparable with that of her husband's death.

And what of her father's legacy? "It gets to me that his ideas - mainly, I'm talking about the North and his concept of dual monarchy - got so quickly ditched. I was never very conscious that he counted a whole lot." She hopes that interest will be revived by a forthcoming biography by Prof John McCarthy, at Fordham University. "He has said, I believe, that he regards my father's work asvery similar to some of the ideas that have come through in the Good Friday agreement - that it was his capacity to think beyond his tribe that made him outstanding."

FOR O'Higgins's daughter, the North is a preoccupation still. "What I've been looking for is a sense that certain people have been gripped by Ireland's need for forgiveness. But healing may not be our strongest calling," she says.

This faithful Catholic is critical of the institutional Church's slowness in reaching out. Aghast at the spectacle of "two sets of children holed up in their separate schools in north Belfast," she asks: "What were they doing in separate schools? In Ireland, I don't think there is room just to continue on with separate schools and institutions, because the politics are so horrendous. I don't think Christ intended us to live in a little goldfish bowl."

As she celebrates her 75th birthday, Una O'Higgins O'Malley has reason to be proud. She has written a memoir described by Gemma Hussey as extraordinary. In a foreword, Tim Pat Coogan perhaps sums her up best when he writes that she "will always be able to reply with pride to that root situation question of the next generation 'What did you do in the war?' She can say with truth and dignity: 'I tried'."

From Pardon and Protest: Memoirs from the Margins, by Una O'Higgins O'Malley, is published by Arlen House at £14.95 (paperback) and £25 (hardback).