The book is an historical romance, of the epic variety.  It spans a few generations, from the early 1900s to perhaps the 1970s?  It begins in Cornwall in England.  Of course, it revolves around wealthy family that is filled with good-looking people.  There is an accident that maims the well-loved oldest son, heir to the family's great wealth, there is a great deal of international travel and infidelity.  I particularly remember when the family watched the procession for Queen Elizabeth II's coronation in London.  There is a subplot regarding a young woman from Russia who was meant to be brainwashed in to believing she was a relation of this clan, but they didn't quite make it work because she remembered the girl who she was supposed to 'be'.  Also, a subplot is the beginning of international air travel and people's initial mistrust of it.  And of course, someone dies in a plane crash.  I know this is very vague, and I read this book at least 20 years ago.  I don't even remember any names at all!  But any help would be appreciated!