July 1915, the Somme. Private Ken Hoskins has been detailed to a firing squad to execute a deserter from his own company. This experience so appalls him that when he returns to his native Lancashire he joins the nascent Communist Party and on his marriage determines to bring up his children 'in the faith'. His daughter, Pam, later moves to London to become secretary to Harry Pollitt, the Party leader. Summer 1998, London. Ken Hoskins's grandchildren, Margaret and Roy, look alike but could not be more dissimilar. She is a defence analyst; he is a celebrated photographer. She still lives in the King's Cross council flat where they grew up; he occupies a Holland Park mansion. Yet they are unusually close, kept so by dramatic changes in their lives and the subsequent oddities in their upbringing. But things do not develop as Ken Hoskins had hoped, and for Roy and Margaret the past they thought was their inheritance turns out to be something quite different.