'I had to let go, he had his own life'

"We had never heard of her - some people who were more educated knew of her, they had seen her on TV or had read about her," says Muhamed Ribic senior, who is almost blind and walks with a stick. "I can never forget what she has done for my child. She saved his life."

Bianca Jagger, the first and best rock-star wife, is a woman famous only for having divorced Mick and partied her way through New York. You will not be surprised to hear that when she visited Bosnia last week, she was dressed as if for lunch in Manhattan. It would be easy to mock - it was for some. But she is not one of the famous who drop in on the wretched of the earth for a moment of compassion chic. To see her in a cream trouser suit and leopard-skin loafers, walking and talking with a small boy in an orchard near Tuzla, was to witness a chapter in a remarkable and painful story of which she is the heroine.

In 1993, at the height of the war, Bianca spent six weeks in Bosnia. It was a time of horror. And in the gloomy, crowded basement that served as the children's ward in Tuzla hospital, a huge concrete complex that seemed to attract the fire of besieging rebel Serb forces, she saw things she would never forget. "There is one very sad image seared in my mind," she says. "Two little girls, amputees from Zepa. Their legs had been amputated without anaesthetics ...."

But at least they had a mother who could care for them. Muhamed Ribic, who was eight at the time and suffering from a congenital heart defect that could not be treated in Tuzla, lay in bed alone, day after day. He had no visitors and did not speak much, in stark contrast to Sabina, a beautiful, blonde 12-year-old who was suffering from leukaemia.

Bianca went to see him carrying a Hi-8 video camera that fascinated him and which prompted a strange kind of communication - with no shared language. "I became very attached to him," she says. "And he came to trust me."

She visited Muhamed and Sabina every day and their doctor, Hatidza Zunic, asked her to help evacuate the children for medical treatment. It was clear that both would soon die if they remained in Tuzla. Sabina's mother would come, too, but Muhamed's would not. At the last moment, she agreed to place her son in Bianca's care, encouraging a relationship that would go far deeper than either could know.

"It was life and death," she explains. "When you live with a child who's on the verge of dying and they trust you, and they believe so deeply that you are going to help them, to save them, that responsibility is so enormous, and the risk in leaving Bosnia together - it creates a bond, almost like a family bond."

Despite her considerable charm, not to mention influential friends, Bianca could not persuade the UN to fly her charges out. With time running out for Sabina, she set off on the hideous and dangerous two-day journey to Split along dirt tracks, over mountains and through front lines. By then, Sabina was too ill to fly on to the United States. She died two days later.

"I can't explain what it means to people in a state of distress to go to America, the Promised Land," says Bianca, the bitterness still with her three years on. "When I had to break the news to Sabina, I knew she would give up. In some way, to her, America meant life, the hope to go on living."

She flew on to New York with Muhamed. "I was so upset and angry, because I thought we had the capacity, the international community, to save these children from the war ...."

She knew her efforts would be dismissed by some: "So many people questioned the validity of what an individual can do" - particularly, one suspects, when that individual is a socialite divorcee. "But I have a profound belief that individuals can make a difference."

In changing Muhamed's destiny, she grew into her adopted life as a human rights activist connected to Amnesty International and Human Rights Watch, an advocate for those whose interests are of little importance to the world and the men who run it.

"It has a lot to do with who I am and where I come from," she says. "I was born in the Third World and have striven to speak for those who have no voice. Muhamed was the essence of that, a little, sickly child who had been abandoned in the hospital and was not very friendly to strangers."

Muhamed underwent a serious operation in New York, and Bianca slept in his room. He was sometimes aggressive to staff, yet endearing, bright, and very attached to her.

She understands the confines of illness - she spent a year unable to walk after having been hit by a car - but says that her mother's experience as a woman in the macho culture of Nicaragua is what really helps her to understand the powerlessness felt by people like Muhamed.

The operation was a resounding success, and Muhamed was well for the first time in his life. The emergency was over, but not the war. Muhamed moved into the Jagger home in New York, but he missed his parents and she agonised about the future.

"If he had had no parents, yes, I would have adopted him; but he had parents and he wanted to go back to them."

This was impossible - Tuzla was starving - but eventually she managed to win permission for the Ribic family to come to the United States.

Eight months after arriving in the US, Muhamed moved from Bianca's home to Hackensack, New Jersey, with his parents and Sahba, his older sister. "I was torn, because of course I became very attached to Muhamed and I think Muhamed became attached to me," she says. "I had to reason with myself that I had to let go of Muhamed and that he had a life of his own." But that life was not to be in New Jersey.

Mr and Mrs Ribic, a working-class couple from small-town Bosnia, did not feel at home in Hackensack; the war was over and there was no reason to stay. Bianca, who had wangled green cards for the parents, begged them to reconsider, fearful of how they would cope in the miserable poverty of post-war Bosnia.

The Ribics were a problem family right from the start; worse, they have been profoundly damaged by the war. Sahba, who is 12, will not speak English despite more than two years at school in New Jersey; Muhamed can barely read or write, since his education was neglected during his illness. Sahza, their mother, has had psychological problems and so, it seems, has her husband.

New Jersey was not the answer: "We realised we had no future there ... we did not feel safe or secure in the US, we felt we were under a lot of pressure and we almost had a breakdown," Mr Ribic says. His wife and daughter, in particular, wanted to go home, so Bianca made the arrangements and has travelled with the family from New York to Tuzla.

Last week I watched Bianca and Muhamed walking together in the dappled garden of his grandmother's house in a village close to Tuzla. He ran off to help his uncle crush home-grown apples in a magnificent wooden contraption designed to pulp fruit for jam-making, and she watched, pensive, before turning to the relatives crowding around offering juice.

Coming home, Bianca knows, means the Ribics will muddle through like everybody else here, surviving, it seems, on thin air and the family network. But she wants Muhamed to live, not just to survive. There is love between them. As Bianca prepares to leave the garden, she and Muhamed wander off for a final chat. The other women, dressed in the long skirts and headscarves of the Bosnian countryside, weep as they hug her in farewell. She is composed, and Muhamed is nonchalant.

"She's a cool friend, a best friend," he says. He liked living in the US, and is easy speaking English or Serbo-Croat. He refuses to be photographed with his father, and boasted with enormous pride of having watched an R-rated movie in America. He hopes to visit Bianca, "but I don't know how much money I will have to pay. It's a lot of money for a ticket."

She wants him to come, too, but she wants also to give him the space in which to return to his own life.

Five days in the city have taken their toll, and she looks tired - though still spectacularly attractive. We leave for Sarajevo, where she will spend a couple of days meeting officials and old friends, a day later than planned so that she can take Muhamed and his mother to the hospital one last time, part of her campaign to ensure that someone in Tuzla will keep a medical eye on the boy.

He changed her life, she says, particularly in her work. Her fame helped her to find doctors willing to treat him in the US, but celebrity is a double-edged sword that has hampered her attempts to be taken seriously.

Those of us who have worked in Bosnia and other war zones are familiar with the do-gooders, who often do more harm, and with the bureaucracies that want action embellished by red tape. Ms Jagger, by contrast, impressed some cynical and knowledgeable journalists with her grasp of the situation in Bosnia and her willingness to ask questions. She did not seek publicity on her trip - though she agreed to let me tag along some of the time - and refused to let the television cameras politely pursuing her go anywhere near Muhamed.

Would she do it all again? There is a long pause.

"Probably. I'd be very careful to make sure that the mother accompanied the child from the beginning. I think it is crucial," she says, her smile twisted a little. "I feel that in practical terms I have come to the end of a mission, but in emotional terms I have not, because I love Muhamed and I will always worry for his future and hope that he will be happy."