I had the idea that I wanted to be a writer aged about 11 or so, and I made a book, which I illustrated and gave to my mother as a present. I must have been expecting some affirmation from her of previously undiscovered genius, because her reaction, though perfectly civil, failed to satisfy me, and I decided - and I remember thinking this exact phrase - that being a writer would be "too lonely a profession". Instead I decided I'd be an actress, based on nothing but my assumption that I could leave school early and bypass university. I never wanted to study. I wanted to make things. And so I singlemindedly followed this path.

Without really paying it much attention, I did a lot of writing as an actress. At drama school we were encouraged to write in-depth biographies for each character, something I often found easier than the performances. Then, once out in the world, to give some structure to my unemployed days, I enrolled in a creative writing class run by the novelist Michèle Roberts. I know now how rare it is to be with a group of people who are doing something purely for the pleasure of it. No one, as far as I knew, had ambitions to be published; everyone just loved being in that Monday morning classroom, finding, as the course promised, our voice. The following year I enrolled in an evening class, but this time the room was full of ambitious working people, the teacher brusque and critical. She asked each of us to write a long piece and read it out to the class, and so, never having written anything longer than 500 words and convinced I had nothing to write about, I wrote a story based on my Moroccan childhood. "I think you should continue with that," came the terse response, which I accepted as the high praise it was.

It took me another four years to discipline myself to make any real headway. By the age of 26 I had 40 pages and two pieces of advice from an Arvon tutor: one, to work on my novel every day; and two, to abandon the complicated structure of flashbacks I'd adopted, and tell my story from the beginning. But I didn't know how to do either of these things. I didn't know how to resist all the myriad distractions of my life and I didn't know the whole story of the 18 months I'd spent travelling with my mother and sister in north Africa. Just make it up, the tutor suggested, and so one day I began. Or to be truthful, I was forced into beginning, after a miserable six months during which, reeling with heartache from a split with a boyfriend, I'd taken a job that involved removing my clothes and performing naked on the Edinburgh stage, wearing nothing but a blond wig. Now here I was again, home, unemployed and alone.

Right, I decided, I had to take some control, and so I resolved to work on my book every morning for three hours, until something fantastic happened (ideally a world tour with the RSC) that meant I would be allowed to stop. At first it was a struggle, and every day I had to force myself to start, but soon, as my memories revealed themselves, and my imagination ignited, I was caught up in a secret world of my own making. I'd never been so happy. I'd been telling stories all my life, often just to myself, and now they came pouring out. I wanted to show what it had been like to be the conventional child of rebellious and unconventional parents, the confusion and humour of the situation, the warmth and closeness, the safety and fear of being in a foreign country, the beauty of that country, the kindness of the people. I visited my mother regularly and listened, a tape recorder between us, while she remembered her earlier life for me. As soon as I got home I'd turn her memories round and imagine what my protagonist, a girl of five, would have been thinking.

And the more I thought about Morocco, the more I remembered it. The sunsets, the smells, the scorched earth, the cool of the courtyard tiles. It did occur to me that it might be easier to go back there, but I was too superstitious. What if the minute I stepped off the plane all my memories evaporated? I decided to reward myself with a research trip once the book was finished, and 14 months later I did go back. I stood outside the tiny airport and looked up at the stars glinting in the velvet sky, breathed in the dust and heat smell of the night, and allowed myself to hope, wildly, that I'd got it right.

· Next week John Mullan will discuss readers' responses to the novel

In Hideous Kinky, the narrator's mother and her friends are escaping England for an alternative life in Morocco. There is to be nothing "conventional" for them. Their relationships, therefore, are not exactly predictable. In the first chapter, there is some peculiar triangle involving Maretta, who sits silently in the back of the camper van; John, who "was Maretta's husband"; and the child narrator's mother. The narrator recalls overhearing John say that he brought Maretta "at the last minute only because she wasn't well".

"'She'll be all right once we get to Marrakech. She'll be all right.' He put his arm around my mother's waist. 'I was married to her for four years. I should know.'"

So he was her husband, past tense? And is she silent through fury as she witnesses him carrying on with another woman? Or is that arm around the waist just fraternal?

Most novels are in the business of explaining human relationships. The most ambitious novels are in the business of making them seem complex and credible. So it is unusual to have a novel that designedly leaves adult relationships unexplained. Freud's four-year-old protagonist does her best to find out what is happening, but her child's questions never solve our puzzles. Finding her mother "crying over the onions", she asks about John's return to England. Maretta was sent back by the hospital and John followed.

"'Did they send John on an aeroplane?'

'No. They didn't send him. He went.'

'Why?'

'Because he wanted to.'

'Didn't we want to?'"

No, her mother tells her, "we" do not want to go "home".

Is "Mum" using the onion chopping to hide her distress? Has Maretta reeled her man back in? We can only imagine the adult arguments behind the scenes. Much later the protagonist hears from a letter that John and Maretta "are having a baby". "Haven't they got one already," asks her mother's friend Linda, who has come to stay with them in Marrakech.

"'Yes.' My mother lowered her voice. 'But she was taken into care.'

Linda sighed. 'I remember now.'"

The novel's fragments of adult conversation are full of implicit understanding. But nothing too much can be said in front of curious children.

"'What's care?' Mum folded up the letter and slipped it into its envelope. 'And that's enough Fanta for one day,' she said." The reader is allowed to glimpse a whole case history, but then the door is closed. The protagonist's mother never has to answer any of the more probing questions.

"Mum" is a peculiar mixture of carelessness and resourcefulness. She leaves her six-year-old daughter behind in Marrakech with a family she does not know while she travels to Algeria to see a Sufi holy man. Yet the challenge of surviving in Morocco with little money and no command of the language hardly flusters her. One of her techniques is to find a man, which means more puzzles about adult relationships. First there is Luigi Mancini, "a prince", the narrator assures us, who has them to stay in his "palace". Will he "ask Mum to marry him?" The protagonist and her sister try to lip-read the two adults' intimate talk as they walk in the garden, but we are none the wiser.

Luigi disappears from the book, but "it was not long before another suitable candidate presented himself". This time it is Bilal, who is Moroccan, and who "came to live with us". "Is Bilal my dad?" the protagonist asks her mother. He takes them to visit his family in the mountains, as if he is making their relationship official. Bilal tells Charlie, an Englishman they meet: "My wife is English." "I wondered if they'd got married and forgotten to say." Charlie addresses her as "the English wife" and we get another of the novel's knowing adult exchanges. "Mum laughed and looked at Bilal. 'Well, not quite . . .'" The uncertainty about these relationships is not just a consequence of the child's naivety. It also seems her mother's tactic, her way of attaching herself while keeping herself free, her special skill.

She and Linda do not just have obscurely fathered children. They have left behind relationships whose only evidence are the letters they receive. Linda reads out one from her mother, who has just found out about her baby and writes lamentingly that she is her only grandchild, yet "we don't even know her name". "Mum and Linda laughed so hard that I had to pat their backs to stop them choking." Are they callous and heartless, or do they share some knowledge of how badly their mothers have behaved to them? Or is it funny? Linda's baby is called "Mob" - because "her father was an anarchist".

Of course relationships are opaque in Hideous Kinky because the story is told by a child. Yet this is pleasing for the reader rather than frustrating. It draws us into the business of inference, comic or melancholy. And it fictionalises something we recognise from adult life: that much of the time we are just guessing at the nature of those relationships that novels usually like to explain.

· John Mullan is professor of English at University College London. Join him and Esther Freud for a discussion on September 3 at the Newsroom, 60 Farringdon Road, London EC1. To reserve a ticket email book.club@guardian.co.uk or phone 020 7886 9281.