Hephzibah Menuhin was seventeen, already famous for her musical partnership with her brother Yehudi and shortly to play her first solo concert at Carnegie Hall, when she made the quixotic decision to marry and move toAustralia. She intended to abandon her music career entirely in order to live on the other side of the world with a young man she hardly knew. Talented, intelligent and beautiful, Hephzibah was on top of the musical world. Critics and audiences asked then, and afterwards, what on earth she thought she was doing.

It was a question I frequently heard from my father, a great admirer of the Menuhin family from his teenage years. As a university student in 1935 , he had saved enough from his allowance for a balcony-seat ticket to one of Yehudi's concerts at the Sydney Town Hall, something he described as one of the great musical experiences of his life. He also admired Yehudi's sister Hephzibah, considered by many to be as brilliant a pianist as her brother was a violinist. 'Why someone with a talent like that would bury herself down in Victoria I'm blessed if I know,' my father would say.

Hephzibah, Yehudi and their younger sister Yaltah had all shown dazzling musical gifts from a very early age. But of the three, only Yehudi went on to a full career as a professional musician. What happened to his sisters? I began to wonder whether Hephzibah and Yaltah Menuhin exemplified the observation of the English critic Cyril Connolly: 'Those whom the gods would destroy they first call promising.'

A fascination with the fate of those who show great early talent remained with me. Then in 1981 I happened upon a radio documentary commemorating Hephzibah, who had died earlier that year. Produced and narrated for the Australian Broadcasting Commission's The Coming Out Show by the influential feminist commentator and academic Eva Cox – who was, I learned for the first time, Hephzibah's stepdaughter – it featured interviews with Hephzibah and with those who had known her. I heard her light, precise voice with its slightly Germanic vowels and hint of an American drawl as she spoke about things that were important to her, and I was drawn to her warmth, thoughtfulness and humour.

I thought little more about her until 1999 , when SBS television screened Hephzibah, a feature-length documentary by Sydney filmmaker Curtis Levy. This was a fuller portrait still, drawing on many of Hephzibah's letters and showing her to be a clear and expressive writer. It revealed more about the second extraordinary choice Hephzibah made in her life: to leave her wealthy husband and family in Australia to live and work with an impecunious Viennese sociologist in London. I began to wonder how a woman like Hephzibah had made sense of the world; how her exceptional childhood had affected her career, relationships, family, and the choices she made. I wondered too about the scope and nature of her talent; wanted to understand what, given the apparently low value she placed on her career, her musical gift meant to her.

A woman as talented as Hephzibah Menuhin, and one who subverts expectations as determinedly as she did, is worth the attention of any biographer. Yet surprisingly little has been written about her. Yehudi naturally dominates biographies with 'Menuhin' in the title, in most of which Hephzibah, along with Yaltah, is little more than a member of the supporting cast. She comes to life briefly in Yehudi's graceful autobiography Unfinished Journey ( 2001 ), although mostly as his loyal lieutenant and 'wonderful follower'. Her father Moshe Menuhin's The Menuhin Saga ( 1987 ), which purports to be the fami-ly's history, is really the story of Yehudi and his career; Hephzibah and Yaltah are only lightly sketched. Robert Magidoff 's 1955 biography of Yehudi has some fascinating material about the three Menuhins as children, evidently taken from people who knew them at the time. However, like Menuhin: A Family Portrait by Tony Palmer ( 1991 ), the main character, after Yehudi himself, is Marutha, his mother. The most thoroughly researched Menuhin biography, by Humphrey Burton, is a detailed account of Yehudi's life with comparatively little about Hephzibah.

In all these books, Hephzibah is most fully described as a child – the golden-haired girl, the second member of the trio of Yehudi-and-Hephzibah-and-Yaltah. Menuhin biographers spend little time on her after her marriage; the rest of her story is barely mentioned, although its extraordinary twists and turns are deeply embedded in what Hephzibah's second husband described as 'that shared dark childhood'.

In the early 1980 s feminist biographers were reclaiming and retelling the stories of women – writers, artists, aviators, doctors, many others – who, while well known in their time, had never been given their due by posterity, largely because men had written the history books. And here was Hephzibah Menuhin, a brilliant woman overshadowed as a musician by her brother but who found new and unexpected directions for herself. Why her story has not been published before now is difficult to understand.

Like all life stories, Hephzibah's feeds into wider narratives, in her case themes of twentieth-century history. Her parents were born in Russia in the 1890 s and were part of the great Jewish diaspora. Leaving Russia under the threat of Czarist pogroms they went to Palestine, where the campaign for a Jewish homeland was just beginning, and then to the United States where, with thousands of other immigrants, they made new lives. Hephzibah's decision to live in Australia brought her face to face with isolation in a country she found culturally backward at first, but which finally revealed unforeseen riches. Her postwar visit to the Theresienstadt concentration camp forced her to confront the meaning of her own Jewish heritage, prompting a realisation that had enormous consequences for the rest of her life. Her move to London came at a time when certainties were being questioned, when establishment complacency was giving way to protest, and England's class-based structures were beginning to weaken. It was a period of racial conflict, the rise of feminism and the peace movement, of change and renewal of many kinds.

Born into the aristocracy of musical talent, knowing that success in that world was hers for the taking, Hephzibah Menuhin wanted something different, something more, from life. She drove herself to make certain choices that were often hard, both for herself and for those who loved her, and sometimes her decisions seem nothing short of perverse. And while she was not destroyed by the gods, she nevertheless paid a high price for finding and taking what she needed.