Frenchman's Creek by Daphne Du Maurier

A classic story about an unhappy mother and wife who escapes to Cornwall and finds illicit love and adventure.  I read this in Cornwall which added to the atmosphere but it is a great read wherever you are.  The main character, Dona, is easy to like and this makes the plot more engrossing.  The writing is very good, with some wonderful descriptions of the Cornish coast and countryside.  Definitely worth reading.