So already we were straying from our intent - to bring Valentino's story to the general reader. Without sensory detail or dialogue, the book would be parched, and likely to reach only those already interested in the issues of Sudan. I was holed up in a cabin a few hours north of San Francisco, trying to figure out the book, when, after wrestling with all these problems for the year or so after our trip, I finally gave up. I was cornered. I couldn't make an interesting non-fiction account of his life - I do believe another writer could, but I personally couldn't - and a simple oral history wouldn't add anything significant to the material out there. I didn't know how I would tell Valentino that the thousands of hours he'd given to the process were for nothing, but I knew that I'd spent two years on it and didn't feel any closer to doing justice to his life and everything he wanted from the project.

Yet hours after I had given up - and I truly gave up - something occurred to me. Or many things occurred to me. First, I remembered that, at the refugee camp in Kakuma, in northern Kenya, Valentino had been part of a theatre group whose mandate was to write and perform one-act plays to educate the residents of the camp in various issues - HIV/Aids, gender equality, conflict resolution. So he knew that one usually needed to adapt the facts of life and shape them in such a way that they came alive in the minds of an audience.

By the same token, I realised that so many of the books I'd brought with me for inspiration, and the books I'd been reading on the shelves of this book-filled rented cabin, were novels. The books about war and upheaval that I'd turned to again and again, and that best (in my opinion) communicated the realities of war, were in fact novels: The Naked and the Dead, The Things They Carried, The Painted Bird, Catch-22 - War and Peace, for Christ's sake. Only with a bit of artistic licence could I imagine the thoughts in Valentino's mind the first day he left home, fleeing from the militias, never to return. Only in a novel could I imagine the look on the face of the man who rescued Valentino when he became entangled in barbed wire one black night in the middle of his journey to Ethiopia. Only in a novel could I apply what I had seen in the various regions of southern Sudan to describe the land, the light, the people.

I knew this was the only way I could do the book, but I put off calling Valentino with the idea. Although we'd never disagreed on anything involving the project, I thought he might think this step too extreme. I stalled for a few days, but when we finally spoke, he understood completely. "You have to be a writer," he said. "Do it the way you think it will best reach people."

I started anew, right then, finally thinking I could fulfil my promise to Valentino. The first thing I did in my new method was to reimagine Marial Bai, before the war. The book needed a sense of the town - and, by association, hundreds of similar places - before the coming of the conflict. The book needed to demonstrate, step by step, how the war unfolded, through the eyes of a tiny boy in a busy market town. Through my own research, I'd been able to pinpoint the series of events that led to all-out civil war, and combining these milestones with Valentino's memories, finally we were able properly and vividly to convey how the utopian dreams of a small group of well-meaning rebels can engulf an entire country in two decades of mayhem and mass murder.

Sudan had been in a state of civil war off and on since its independence from Britain in 1956; the conflict that swallowed southern Sudan began in 1983, when the Sudan People's Liberation Army, aiming to represent the needs of southern Sudan, rose up against the northern, Arab-dominated government in Khartoum. The SPLA and its leader John Garang demanded a greater share of the country's resources, better infrastructure and more autonomy for the south, among other things. In response, the government of Sudan instituted the "to catch a fish, drain the pond" method of warfare. The government armed and unleashed tribal militias upon hundreds of villages in the south. The militias - then known as the murahaleen but not dissimilar from the Janjaweed now at work in Darfur - were urged to depopulate the south, to wreak havoc and terror, and they were paid both directly and in booty. Whatever the militias could carry off from the villages was theirs to keep. They swooped into villages by the hundreds, killing men, raping women, burning homes and crops, and abducting girls and boys to be bought and traded as servants and sex slaves in the north. The Sudanese government also bombed southern villages with Russian-made Antonov planes and obstructed the delivery of aid and food to the region, causing hundreds of thousands of deaths. The level of mayhem at this stage of the war defies description.

But when Valentino and I met, the SPLA and the government of Sudan were negotiating a peace; the African Union, the US and the wider international community were involved in bringing all the parties to the table. The ceasefire they established has lasted to this day. In 2005, the government of Sudan and the SPLA signed the Comprehensive Peace Agreement, granting the south far greater autonomy, half of the country's oil profits and, most importantly, the ability to secede, should the people vote to do so, in 2011.

The strangest thing about all this is that while this peace agreement was being negotiated, the first killings were taking place in Darfur. A rebel group in western Sudan, the Sudan Liberation Army (SLA), rose up because of the negotiations going on between the SPLA and the government. The SLA (and, later, other groups) felt that if the SPLA could be successful in fighting for their share, they might as well give it a shot. And incredibly, while negotiating with the south under the watchful eye of the international community, the Sudanese government was allowed to revive its vicious civil war tactics for use against the civilians of Darfur. Again to punish a region's rebel movement, the government unleashed great fury upon its defenceless citizens. Again there were indiscriminate bombings, and again there was a brutal government-funded militia - the Janjaweed, known by Americans who work in the region as the KKK of Darfur, tasked with "cleansing" the region of black Muslims.