Ralph Messenger is a man who knows what he wants and generally gets it. Approaching his fiftieth birthday, he has good reason to feel pleased with himself. As Director of the prestigious Holt Belling Centre for Cognitive Science at the University of Gloucester he is much in demand as a pundit on developments in artificial intelligence and the study of human consciousness - 'the last frontier of scientific enquiry'. He enjoys an affluent life style subsidised by the wealth of his American wife, Carrie. Known to colleagues on the conference circuit as a womaniser and to Private Eye as a 'Media Dong', he has reached a tacit understanding with Carrie to refrain from philandering in his own back yard.This resolution is already weakening when he meets and is attracted to Helen Reed, a distinguished novelist still grieving for the sudden death of her husband more than a year ago, who has rented out her London house and taken up a post as writer-in residence at Gloucester University, partly to try and get over her bereavement.Fascinated and challenged by a personality and a world-view radically at odds with her own, Helen is aroused by Ralph's bold advances, but resists on moral principle. The stand-off between them is shattered by a series of events and discoveries that dramatically confirm the truth of Ralph's dictum, 'We can never know for certain what another person is thinking.'