In the brief golden years of the Edwardian era the McCosh sisters--Christabel, Ottilie, Rosie and Sophie--grow up in an idyllic household in the countryside south of London. On one side, their neighbors are the proper Pendennis family, recently arrived from Baltimore, whose close-in-age boys--Sidney, Albert and Ashbridge--shake their father's hand at breakfast and address him as "sir." On the other side is the Pitt family: a "resolutely French" mother,...