What really happened to Mum?

How does a book come into being for a writer? My first book, an account of a mysterious death in a wildlife park in Kenya, was commissioned after I had covered the story as a journalist. My second novel, based on the history of my father's family, was inspired by the discovery of a manuscript written by my great uncle, though the way to write it came to me on a walk on Hampstead Heath. I still have the scrap of paper on which I scribbled down the plan of that novel.

Other books seem to have been inside you all along, to have shaped you even before you begin to shape them. It was reading an article about the suicide of Nicholas Hughes, the son of Ted Hughes and Sylvia Plath, seven years ago, that prompted me to write the article about my own mother's suicide that grew into my latest book. But where did the book really begin? With my brother's sudden death from a heart attack three years before that, which unearthed older feelings of grief in me the way an earthquake exposes things long buried? With a subsequent heart attack of my own, which brought me face to face with my own mortality?

Or did the book begin another decade earlier, when clearing out my grandparents' house I found my mother's suicide note and an old newspaper report of her inquest, which told me that she had dropped me at my nursery school before driving on to the friend's flat where she gassed herself? Or was it when I was 16 and my father took me for a drive to tell me that her death had been suicide? Or the morning after her death when he sat my brother and me down on his bed to tell us the untellable?

I think in some way that this book began then, in a corner of my four-year-old mind. In the house in which I grew up we never spoke about my mother and, in time, I lost all memory of her, but I never forgot that she had existed, never lost the feeling of her absence.

I grew up in the visible world, with a new stepmother, two new sisters, a house eventually full of noise and people, but some part of me always existed in that other, invisible world, with the ghost of my mother.

As a boy I had heard stories about her youthful mischief

The first few months of researching her life was as hard as anything I have done. The family taboo was so powerful that I had to summon all my courage before each phone call or meeting with one of her friends. As a boy, all I had known of her were a handful of stories my grandmother told of her youthful mischiefs - locking the neighbour in her chicken shed until she promised to stop hitting her son, driving her car on the pavement - and in my imagination she was a character out of a fairy tale. Hearing about the real woman, that she could be selfish and melodramatic, was so distressing that I almost gave up my quest before I had properly started. One of the stories my grandmother told was about my mother having an "affair" with her headmaster at her progressive boarding school when she was fifteen. I soon began to think of this in more disturbing terms and it wasn't easy to be told about her walking down the corridor in the evening from her dormitory room to the headmaster's study - even more so as I had a daughter of a similar age at the time. I found myself reacting then like a father more than a son.

For a time, I was obsessed with the headmaster, convinced that he held the key to my mother's death. I researched his life and found that he had earlier led four schoolboys to their deaths in a snowstorm in a German forest. In the process, I learned more about my mother's teenage love life than any son should really know, and it was a relief in the end that I never found out exactly what happened in that study.

There were also some magical moments, though. The time, for instance, when I was met at the train station in Bristol by one of my mother's friends. She looked me up and down and said, "You look like her." I was 47 and it was the first time anyone had ever told me that I looked like my mother. I remember going home that evening and studying my face in the mirror.

Meeting so many people who had known and cared about my mother was a moving experience. It was fifty, sixty, sometimes seventy years since they had seen her, and their memories had faded over time. But, from the one or two new details each of them gave me, I began to piece together the story of my mother's life, to get a sense of her, to come, for the first time, to feel that I knew her.

After she died, most of her possessions and papers were thrown away, but there were still paper trails to follow. I found files for her in the library at the Royal Academy of Dramatic Art, where she had trained for a year-and-a-half to be an actress, and in the archives of Bedford College, a woman's college in Regent's Park in the 1960s, where she had studied sociology.

Even the smallest details told their own stories. Her application to RADA had been signed by the headmaster, as "Referee for Character and Respectability." On her application to Bedford College, when she was 19 and newly married, my father signed as her guardian.

Some clues were hidden in plain sight - such as books on the shelf in the house where I grew up that had been hers. Most probably, they hadn't been opened since she died and inside I found a draft of a review, as well as her signatures, her underlinings and scrawled comments in the margins. In the back of a filing cabinet, I found a wad of old papers that my stepmother had stashed away when she moved in with us.

There were a couple of notes my mother had written and some letters from her publishers: her first and only book, The Captive Wife, a study of the conflicts of young mothers, was published a few months after she died. Among the papers was a stack of cheques returned from the bank, as happened in those days.

From these mundane documents I was able to compile a sense of her life in her final months - her membership of the Hornsey Labour party, a visit to the Marie Stopes clinic, a shopping trip to the Zing Boutique.

Most important, and most moving, were a cache of letters she had written to her best friend between the ages of fourteen and twenty. I had heard about these several years earlier but had been told that they were lost - to my despair, for I had no memory of her voice, and almost no personal writing of hers. Her book, though her words, was an impersonal, sociological study.

So when I did finally get hold of her letters it wasn't surprising that I was at first disappointed that they revealed so ordinary a girl. But as time passed I realised that this was what I wanted, wasn't it? To know the real girl, the real woman. And, again, I found that when I looked closely there was much in the details.

I had heard how "dramatic" she could be, but her letters were more wry than melodramatic and even earnest at times. She could be selfish, but she could also be generous towards her friends. And to my delight I found that my mother was funny, that her sense of humour was similar to my own. "Sonia only had one line," she wrote of her correspondent's sister whom she had seen in a play, "but she was excellent and showed great signs of talent." Of her own studies to be an actress at RADA she wrote, with a little smile I imagined: "I don't want to go out much as I have a lot of work to do - lying on the ground breathing in and out."

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