When Michela Wrong's Kenyan friend John Githongo appeared one cold February morning on the doorstep of her London flat, carrying a small mountain of luggage, it was clear something had gone very wrong in a country regarded until then as one of Africa's few budding success stories.

Two years earlier, in the wave of euphoria that followed the election defeat of long-serving President Daniel arap Moi, John had been appointed Kenya's new anti-corruption czar. In choosing this giant of a man, respected as a longstanding anti-corruption crusader, the new government was signalling that it was set on ending the practices that had made Kenya an international by-word for sleaze.

Now John was on the run, having realised that the new administration, far from breaking with the past, was using near-identical techniques to pilfer public funds. John's tale, which has all the elements of a political thriller, is the story of how a brave man came to make a lonely decision with huge ramifications. But his story transcends the personal, touching as it does on the cultural, historical and social themes that lie at the heart of the continent's continuing crisis.