Saturday, February 15, 2003. Henry Perowne is a contented man - a successful neurosurgeon, the devoted husband of Rosalind, a newspaper lawyer, and proud father of two grown-up children, one a promising poet, the other a talented blues musician. Unusually, he wakes before dawn, drawn to the window of his bedroom and filled with a growing unease. What troubles him as he looks out at the night sky is the state of the world - the impending war against Iraq, a gathering pessimism since 9/11, and a fear that his city, its openness and diversity, and his happy family life are under threat. Later, Perowne makes his way to his weekly squash game through London streets filled with hundreds of thousands of anti-war protestors. A minor car accident brings him into a confrontation with Baxter, a fidgety, aggressive, young man, on the edge of violence. To Perowne's professional eye, there appears to be something profoundly wrong with him. Towards the end of a day rich in incident and filled with Perowne's celebrations of life's pleasures - music, food, love, the exhilarations of sport and the satisfactions of exacting work - his family gathers for a reunion. But with the sudden appearance of Baxter, Perowne's earlier fears seem about to be realised. Ian McEwan's last novel, Atonement, was hailed as a masterpiece all over the world. Saturday shares its confident, graceful prose and its remarkable perceptiveness, but is perhaps even more dramatically compelling, showing how life can change in an instant, for better or for worse. It is the work of a writer at the very height of his powers.